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Forensic Science Course for BLS 201 Lecture Notes

Introduction The Development of Forensic Science

The word “forensic” derives from the Latin word for “forum”, meaning public. It has taken on a meaning associated with courts of law, which are public. Thus, in our culture “forensic” really means “pertaining to the judiciary”. Thus, forensic science is the application of the areas of science (and particularly natural science) to both criminal and civil law.

The use of science in enforcing law is relatively antique. In ancient Babylon, fingerprints in clay tablets were used as a way of signing contracts; in 8th century China, thumbprints and fingerprints were employed similarly. At least as early as the 14th century, a Persian doctor observed that no two fingerprints on contracts seemed to be the same.

As regards criminal activity, in 1248, a book, Hsi DuanYu (the Washing Away of Wrongs) published by in China, described how to distinguish drowning from strangulation. It was the first recorded application of medical knowledge to the solution of crime. In 1609, the first treatise (dissertation/thesis) on systematic document examination was published in France. Then in 1784, one of the first documented uses of physical matching saw an Englishman convicted of murder based on the torn edge of a wad of newspaper in a pistol that matched a piece remaining in his pocket.

However, with a few exceptions such as those mentioned above, Forensic Science as it applies to criminal and civil law was by-and-large born in the 19th century, following the development of chemistry as a distinct science in the mid-to-late 18th century.

One of the most famous early applications involved arsenic poisoning. Arsenic(III) oxide, As2O3 , was first produced commercially in the 8th century as a result of refining ore in iron and lead mining. It became the poison of choice for many over the succeeding centuries. As III oxide is colorless, odorless and tasteless. Its symptoms mimic natural diseases; acute arsenic poisoning resembles gastroenteritis (which is the inflammation of the mucous membrane of the stomach and intestines), while chronic arsenic poisoning presents a combined picture of stomach upsets, peripheral neuritis (which is the inflammation of a nerve or group of nerves, characterized by pain, loss of reflexes, and atrophy of the affected muscles) and dermatitis (or inflammation of the skin). The chronic poisoning is much more common– the poisoner gives the victim sublethal doses over a long period of time. The victim will then die after a period ranging from a few months to several years. Besides being colorless, tasteless and odorless, arsenic proved ideal for a long while because its presence in tissues was undetectable. Arsenic poisoning became so popular it was referred to as poudre de succession, or “inheritance powder”.

In 1836 all this changed. In that year, English chemist James Marsh developed a test for the presence of arsenic in tissues. The oxide is changed into arsenious acid, H3AsO3 , by stomach acids, and the acid is absorbed into the tissues. Subsequent treatment of the tissues with Zn liberates arsine gas, H3As. The gas is allowed to pass near a glass disk (or petri dish), where application of a flame causes the arsine to decompose into its elements. The metallic As is deposited as a gray-black film on the glass. The Marsh test (as it became known) is fairly sensitive, being able to detect as little as 0.02 mg As.

In December, 1839, Charles Lafarge, a minor French industrialist, was on a business trip in Paris, several hundred miles away from his home in Le Glandier. He became ill after eating a cake sent to him by his wife. Mrs. Lafarge was a young widow who had married Lafarge through an arrangement by a marriage broker following the death of her first husband. The marriage was an unhappy one. Lafarge returned home, his condition deteriorated, and he died on January 13, 1840. Arsenious acid was found in his stomach, and it became known that his wife, Marie, had bought arsenic as rat-poison from a drug store as far back as mid-December, 1839. She was arrested and sent for trial.

The 19th century saw great strides in developing evidence that would uniquely identify (or individualize) a criminal. The first such system was known as anthropometry, or bertillonage.

Bertillonage was the brainchild of Alphonse Bertillon (1853-1914), who started with the Paris police department in 1879 as a clerk. He had absorbed some scientific knowledge from his father, an anthropologist who had labored to prove that

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each human being had unique variations in physical characteristics. Young Bertillon quickly saw that his father’s academic obsession might have practical value in police work, where detectives had trouble seeing past the disguises and aliases affected by criminals.

Bertillon began using his father’s measuring techniques on arrestees and convicts, fastidiously recording the data on cards. He developed a filing system that put a person in one of three main categories based upon head size. He then subdivided them further according to the dimensions of the left middle finger, and so on down the line, using 11 different bodily measurements.

Bertillon had calculated that the probability of two people having precisely the same 11 measurements was one in four million. A criminal might wear a fake beard or give a phony name, but Bertillon noted that “subjects cannot exercise the slightest influence on their cranium diameters.” His police superiors thought he was a bit crazy until they used his data successfully to identify nearly 800 suspects in three years. In French courts, where suspects were guilty until proven otherwise, proof of a past criminal record was a powerful tool for winning convictions, and Bertillon’s star rose. In 1892 he was appointed director of the newly formed Bureau of Identification of the Paris police. Before long police departments around the world were using bertillonage. Since it was cumbersome for detectives to stop suspects in the street and take their measurements, Bertillon developed a scaled-down, pocket-card version of his system.

What doomed the Bertillon system was unsettling proof of its shortcomings. In 1903 a newly convicted prisoner named Will West arrived at Leavenworth Prison, and was escorted by guards to the office. There they measured his height and the expanse of his arms and wrapped a pair of steel calipers around his head. After that they noted the length of his right ear, left foot, left forearm and selected fingers. They examined the size and shape of his nose, measured the tilt of his forehead and examined his skin for scars and blemishes. All were dutifully recorded on an index card, establishing Will West’s identity under the Bertillon system. As West’s Bertillon measurements were taken at Leavenworth, one of the clerks had a nagging suspicion. Even though West’s paperwork indicated he was a new prisoner, the clerk was sure he had measured him before. Sometime later the clerk checked through the prison files, and sure enough, found an intake file for a William West who possessed the same Bertillon measurements. But there was a problem: This William West, who had been incarcerated at Leavenworth two years before, was still a prisoner. They were two different men. Prison officials summoned both prisoners to the office and were astonished to discover that, although they were not related, they resembled one another as if they had been twins. Then Will West and William West were resubmitted to bertillonage, and their measurements were found to be virtually identical.

A few years later prison officials did find one distinguishing characteristic between the Wests: Their fingerprints were unmistakably different. By then, police departments and prisons across the United States and Europe had switched to the fingerprint identification system.

The English first began using fingerprints in July of 1858, when Sir William Herschel (1792 - 1871), Chief Magistrate of the Hooghly district in Jungipoor, India, first used fingerprints on native contracts. On a impulse, and with no thought toward personal identification, Herschel had a local businessman impress his hand print on the back of a contract. The idea was merely “... to frighten [him]. The native was suitably impressed, and Herschel made a habit of requiring palm prints– and later, simply the prints of the right index and middle fingers– on every contract made with the locals. Personal contact with the document, they believed, made the contract more binding than if they simply signed it. Thus, the first wide-scale, modern-day use of fingerprints was predicated not upon scientific evidence, but upon superstitious beliefs.

As his fingerprint collection grew, however, Herschel began to note that the inked impressions could, indeed, prove or disprove identity. While his experience with fingerprinting was admittedly limited, Sir Herschel’s private conviction that all fingerprints were unique to the individual, as well as permanent throughout that individual’s life, inspired him to expand their use.

During the 1870’s, Dr. Henry Faulds, the British Surgeon-Superintendent of Tsukiji Hospital in Tokyo, Japan, took up the study of “skin-furrows” after noticing finger marks on specimens of “prehistoric” pottery. A learned and industrious man, Dr. Faulds not only recognized the importance of fingerprints as a means of individualization, but devised a method of classification as well.

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In 1880, Faulds forwarded an explanation of his classification system and a sample of the forms he had designed for recording inked impressions, to Sir Charles Darwin. Darwin, in advanced age and ill health, informed Dr. Faulds that he could be of no assistance to him, but promised to pass the materials on to his cousin, Francis Galton. Also in 1880, Dr. Faulds published an article in the Scientific Journal, Nautre. He discussed fingerprints as a means of personal identification, and the use of printers ink as a method for obtaining such fingerprints. He was the first to explicitly recognize the value of latent prints left at crime scenes.

Sir Francis Galton (1822 - 1911)– a British anthropologist, a cousin of Charles Darwin, and the lucky recipient of the information forwarded to Darwin by Henry Faulds– began his observations of fingerprints as a means of identification in the 1880’s. In 1892, he published his book, Fingerprints, establishing the individuality and permanence of fingerprints. The book included the first broadly accepted classification system for fingerprints.

Galton’s primary interest in fingerprints was as an aid in determining heredity and racial background. While he soon discovered that fingerprints offered no firm clues to an individual’s intelligence or genetic history, he was able to scientifically prove what Herschel and Faulds already suspected: that fingerprints do not change over the course of an individual’s lifetime, and that no two fingerprints are exactly the same. According to his calculations, the odds of two individual fingerprints being the same were 1 in 64 billion. Galton identified the characteristics by which fingerprints can be identified. These same characteristics (minutia) are basically still in use today, and are often referred to as Galton’s Details.

Today, the once-famous Bertillon is virtually forgotten, and fingerprinting– despite the recent advent of DNA testing and other innovations– is still the most widely recognized method of individualization. It’s now estimated that the odds are 67 billion to one against any two different persons producing an identical print, and judges and juries throughout the world accept that two identical prints must come from the same person.

The early 20th century saw the beginnings of great strides in medico-biological sciences. In 1901 Paul Uhlenhuth, a German immunologist, developed the precipitin test for differentiating species. He was also one of the first to institute standards, controls, and QA/QC procedures. In 1900, Karl Landsteiner first discovered that human blood divided into four groups– now recognized as A, B, AB and O– and was awarded the Nobel prize for his work in 1930. Max Richter adapted the technique to type blood stains. This is one of the first instances of performing validation experiments specifically to adapt a method for forensic science. Landsteiner’s continued work on the detection of blood, its species, and its type formed the basis of practically all subsequent work. Leone Lattes, professor at the Institute of Forensic Medicine in Turin Italy, developed the first antibody test for ABO blood groups. He first used the test in casework to resolve a marital dispute. He published the first book dealing not only with clinical issues, but inheritability, paternity, and typing of dried blood stains. Even now, the 1915 Lattes test for typing dried blood stains is often used.

Dr. Edmond Locard (1877 - 1966) was perhaps the most famous of the students taught by Bertillon. Locard’s work formed the basis for what is widely regarded as a cornerstone of the forensic sciences, the Locard Exchange Principle. In 1910, Locard persuaded police in Lyons, France, to give him two upper floor rooms and two assistants; he started the first forensics lab. Enthusiasm and research overcame shortages of money and materials and Locard became internationally famous, eventually becoming the founder of the Institute of Criminalistics at the University of Lyons. Dr. Locard, like Bertillon before him, advocated the application of scientific methods and logic to criminal investigation and identification.

While Locard made many significant contributions (to fingerprinting, for example), he is most famous for his Exchange Principle. It was Dr. Locard’s belief and assertion that when any person comes into contact with an object or another person, a cross-transfer of physical evidence occurs. By recognizing, documenting, and examining the nature and extent of this evidentiary exchange, Locard observed that criminals could be associated with particular locations, items of evidence and victims. The detection of the exchanged materials is interpreted to mean that the two objects were in contact. This is the cause and effect principle reversed; the effect is observed and the cause is concluded. Forensic scientists also recognize that the nature and extent of this exchange can be used not only to associate a criminal with locations, items, and victims, but with specific actions as well. In one of several famous cases, three men were suspects in a counterfeiting ring. Locard examined their clothing, and found minute metallic particles. Analysis showed these fragments to be exactly the same alloy as used in the coins. The suspects were arrested and later confessed. Locard’s successes were pivotal in causing police in other nations (notably Austria, Germany, Holland, Sweden and Finland) to starts their own forensic labs.

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Forensic Science Services

Forensic Science is broadly divides into “medical” and “crime lab” components, and these two divisions are frequently separate from one another, both physically and logistically.

Medical Aspects Included here are the following disciplines:

(1) Forensic Medicine, including pathology, forensic pathology, legal medicine and medical jurisprudence. Practitioners

are usually MD’s or Vet Docs and who have specialized certification in pathology or forensic pathology. They are concerned with cause and manner of death and also sometimes are involved in medical malpractice and insurance fraud cases (you will not do this as BLS graduate but it is useful to know what this deals with and will be covered well in Forensic Pathology).

The investigation will focus on answering these questions: Who is the victim? What injuries are present? Why, when and how were the injuries produced? The primary goal is first to determine the cause of death, which is a step-by-step specification of the events or conditions which caused death, starting from the most specific and expanding outward to the more general. Once the cause of death is determined, the manner of death will then be classified as: natural, homicide, suicide, accident, or undetermined.

Time of death can be estimated in several ways. • Immediately after death, the muscles relax. But glycolysis continues for a short while and as ATP is hydrolyzed into

ADP and lactic acid, strong chemical links are formed between the actin and myosin. The muscles become rigid with no associated shortening. This is rigor mortis. Rigor starts within ½ - 1 hour after death, is complete after 6-12 hours, and disappears after 24-48 hours because decomposition causes a lysing of the bonds.

• Livor mortis is the settling of blood into the lower recesses of the body due to gravity. The engorged vessels then rupture, sending blood irreversibly into the tissues and causing the affected regions to turn dark purple-blue. No livor appears in areas which are restricted by clothing or other objects. Livor starts immediately after death and continues for up to 8-12 hours. It can be used to determine if a body was moved postmortem.

• Algor mortis is the gradual cooling of the body to ambient temperature. As a general rule, the body loses 1 to 1½ oF/hour, starting about 1 hour postmortem. This is, however, only a crude estimate as the actual rate of loss can be influenced by myriad additional factors such as size of the victim, clothing, weather, body position, etc. One model gives the approximate number of hours postmortem as (98.4 - rectal temperature)/1.5 .

• If an autopsy is performed, the amount and type of food in the stomach can also provide clues as to the time of death.

• Lastly, upon death the cells on the inner surface of the eye begin releasing potassium into the vitreous humor (ocular fluid). By measuring the potassium levels at several intervals, the pathologist can determine the rate of release, and then work backward to determine the approximate time of death.

For older corpses, the overall condition will be controlled by two competing processes:

• Decomposition, which is the breaking down of the body by action of its own enzymes, and • Putrefaction, wherein the bowels become permeable to their own bacteria, which then start to seep and grow in the

body tissues.

After 12-36 hours, a greenish discoloration will begin in the lower right quadrant. Eventually this hue will spread to the entire body. It is due to the denaturation of hemoglobin via action of the putrefaction bacteria.

After 36-48 hours, marbling will occur. Blood in the vessels is hemolyzed, causing the blood vessels to be outlined in a dark green-black color.

After 36-72 hours the corpse will start to bloat, particularly in the facial and genital regions. This bloating is due to the buildup of the gases which accompany decomposition and putrefaction. After about 3 days, the gases will come pouring out of all the body’s orifices (nose, rectum, vagina, etc.) along with a bloody fluid called purge fluid. After 4-7 days, the skin starts to slip off.

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For corpses which remain undiscovered for long periods, the outcomes can include • Skeletonization, which may take as little as 2 weeks or as long as 1½ years and is common in temperate regions, • Mummification, which is more common in arid regions wherein rapid water loss causes cessation of bacterial

activity; it may start after one week but take up to six months to complete, and • Adipocere formation, which requires the corpse be in a moist and warm environment; it is common in bodies

immersed in water. The fat is converted into free fatty acids which are then saponified. The “skin” has a slippery, greasy feel to it.

(2) Forensic Odontology, or forensic dentistry, which is the application of dentistry to identification of human remains,

especially in cases of mass disaster or in cases where the bodies would otherwise be unidentifiable. The enamel that comprises teeth is the hardest substance within a body, so teeth outlast all tissues and organs. Forensic odontologists may also be called upon to analyze bite marks in criminal cases. Forensic odontology is a subdiscipline of dentistry.

(3) Forensic Anthropology, the practitioners of which are concerned with personal identification of victims based on

skeletal remains. The rate of decay of bones is very slow, requiring many decades or even centuries. Bone injuries can lead to both an identification of a particular individual (by identifying an old break, for example), or, if fresh, can shed clues on the cause and manner of death. Even in the absence of injuries, bones can give clues as to the age, sex, weight and race of the victim. Sometimes faces can be reconstructed from skulls. Forensic anthropologists also develop data bases concerning average body structures as a function of age, weight, race, sex, etc. These data can later be used to start developing the profile of a skeletonized victim, as mentioned above. Practitioners are physical anthropologists.

(4) Forensic Entomology, which can be an important way of estimating time or location of death. Immediately after

decomposition begins, bodies are infested with insects, particularly blow flies, which are drawn to the mucus membranes of the nose, eyes, rectum, vagina and mouth. The eggs are laid in the decomposing flesh and tissue, and these ultimately mature into larvae (3 days), pupae (6 - 10 days), and adults (12 - 18 days). The stage of development of the blow flies is an indicator of time of death, while the precise insects present may provide a clue as to location of death. The analyses are actually quite complicated because the insect life cycles are extremely sensitive to ambient temperatures and other weather patterns.

Crime Lab Aspects These fields are often known collectively as criminalistics, although this name also implies a certain subdiscipline, as well. Included are all of the following:

(a) Criminalistics, which is concerned with all manner of trace and transfer evidence analysis, including fibers, hairs,

paint, glass, soil, blood and physiological fluids (serology), DNA, arson accelerants, explosive residues, drug identification, botanical specimens, and pattern and imprint interpretation. Criminalistics is the broadest area of work which is commonly done at a crime lab. It is entirely possible that Criminalistics will be split up among several smaller divisions, such as a Physical Science Unit (for evidence which is chemical, physical and/or geological in nature, such as drugs, paint, glass, soil, accelerants, residues, patterns and imprints), and a Biological Science Unit (responsible for hair and fibers, DNA, serology, botanical samples, etc.).

(b) Toxicology, which has to do with the determination of toxins and drugs in human tissues and organs, and especially

the role these toxins may have played in death.

(c) Questioned Documents, which includes comparisons of handwriting, printed and copied materials, and analysis of the inks, toners, papers and other materials used to produce the documents. Also included are examinations of indented writings (such as those left underneath a piece of paper which has been written on), obliterations and erasures, and burned or charred documents.

(d) Firearms and Toolmarks, which pertains to firearm identification and comparisons of markings on bullets, cartridges

and other projectiles, especially for purposes of telling whether or not a particular projectile was fired from a particular firearm. Clothing is also examined in order to detect powder residues, as well as to estimate how far away was the weapon responsible for the residue. Toolmark identification is much the same enterprise except that it might include marks left by burglary tools, for example.

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(e) Fingerprints, which includes classification and organization of prints into useable data bases, development of latent prints, and comparisons with known and unknown prints.

(f) Photography, both as a means of recording evidence (perhaps using very specialized films and techniques, like UV, IR

and X-Ray photography) and in the preparation of photographic displays to be used during trial.

(g) Voiceprint Analysis, which involves trying to individualize a voice to a particular person by comparing the sound spectrograph of a suspect’s voice to that found on a recording (perhaps a threat left on an answering machine or recorded surreptitiously during a telephone conversation).

(h) Evidence Collection. Here, a group of highly trained technicians are sent to major crime scenes to document, collect

and preserve physical evidence, which then will be sent to the crime lab for analysis.

These areas of specialization are somewhat arbitrary. For example, Firearms and Toolmarks is sometimes included along with criminalistics, and hairs are sometimes grouped along with forensic anthropology. Toxicology is frequently a subspecialty of the ME’s office. Further, it is unlikely that any one crime lab would have every subdiscipline represented. Also there are other disciplines which are springing up all the time; one obvious one is computer crimes, which is an area becoming increasingly represented in crime labs.

While it takes considerable specialized and advanced training to enter the medical end of forensic science, the typical preparation for a technical crime lab worker is to earn a bachelor’s degree in either biology or (more commonly) chemistry, followed by either a master’s degree in one of these areas or perhaps with simply on-the-job training at a crime lab. However, to rise to a level of significant responsibility in a crime lab will require a Ph.D. degree, often in either chemistry or biology. In all cases, significant continuing education will be necessitated.

Additional Aspects Beyond the medical and crime lab aspects to forensics, there are a few other disciplines that are sometimes encountered, but which don’t fit nicely into one group or the other. Included here would be such things as

Forensic accountants, who specialize in looking for criminal activity on a company’s books or within an individual’s bank account records, and Forensic engineers, who are engaged in failure analysis, accident reconstructions, and the causes and origins of fires and explosions. This course will deal principally with criminalistics (in the larger sense); that is, with the “crime lab”, rather than the “medical” or “additional” aspects of forensic science.

Clime Lab: The Basics

We would like to think that law enforcement tirelessly investigates all crimes, no matter who is the victim or how serious the crime is judged to be. That is not the case. The amount of forensic investigation which is ever possible is largely controlled by decisions made by the original investigators, and these are almost invariably police. Different crimes do not receive the same amount of investigative attention. Frequently, the level of attention is not even proportional to the level of occurrence of a particular crime. For example, burglaries may occur 50 times more frequently than homicides, yet burglary investigations may receive only a small fraction of the time invested in a single homicide. In general, crimes against persons are investigated much more thoroughly than crimes against property.

Unfortunately, decisions about the extent of physical-evidence involvement in the search and investigation stages of a case are usually not made by forensic scientists but by police officers or evidence technicians. There is no guarantee usually that either of these parties do well appreciate the nature or importance of the evidence they take.

Goals of the forensic scientist

Having been presented with a piece of physical evidence, the goals of the forensic scientist are three-fold: (1) identification, (2) individualization, and (3) reconstruction. Only the first of these is common in the other natural sciences. The last two are almost entirely within the purview of forensic science.

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(1) Identification is essentially a classification scheme, common in all science, where objects are assigned to categories

and given names. Different items in the same category all have the same name. Thus, determining whether remains are human or not is a process of identification. Determining whether a particular liquid is gasoline is identification. And determining whether a dried stain is human semen is identification. Identification is accomplished by comparing the properties of the unknown material with the class characteristics of the group, as they have been previously established. Class characteristics are properties that all members of a certain group must possess.

(2) Individualization is common only in forensic science. It involves proving that a particular sample is unique, even

among members of the same class. Individualization may also refer to the demonstration that a questioned sample and a known sample are of a common origin. Here we are operating under the assumption that objects possess individual characteristics that can be used to distinguish them from other members of the same class. For example, proving that remains are human is an identification; proving that the remains are those of Peter XXX is an individualization. Clearly, fingerprints, DNA and dental records provide means of individualization, rather than the more common (but incorrect) notion that they provide means of identification.

Individualization is the most demanding requirement placed on a forensic scientist. For most types of evidence, individualization is an as yet unrealized objective. In the end, individualization is a matter of statistical probability. For example, suppose one is presented a paint chip and asked to prove whether or not it came from a particular car. If the chip edges and area match a scratch on the car, the evidence is deemed conclusive. But what if it doesn’t? Then one must be prepared to say how likely it would be for some other paint chip to have all the chemical and physical properties as the questioned chip. This requires an enormous data base of paint analyses. A similar situation arises in the analysis of fibers, hairs and blood groups. Suppose a suspect was known to have type A blood and a victim had type O blood. The suspect had a drop of type O blood on his socks. One can certainly testify that such a finding is consistent with the suspect causing harm to the victim, but that is about all that can be inferred. To make a more meaningful individualization, one would either have to do a DNA test on the blood, or perhaps be able to quote the probability that any random person might have socks containing a spatter of type O blood. The probability of the latter event is likely much more significant than most people would think.

(3) Reconstruction. Here, the various pieces of identified and individualized physical evidence are put together

inductively to arrive at a hypothesis for the reconstruction of the crime, meaning that one establishes the likely sequence of events. This is difficult to do, and is often impossible. However, it is especially valuable in cases where there is no eyewitness testimony, or where such testimony may be deemed unreliable. Like individualization, reconstruction is unique to forensic science.

Implicitly, another way in which forensic science is unique among natural sciences is its constant interaction with the legal system, particularly law enforcement and the judiciary. This starts with evidence collection, which is often controlled by law enforcement. Then there is the matter of crime labs generally being controlled by (or strongly linked with) prosecutors and/or police. Like other scientists, forensic scientists think of themselves as unbiased and unprejudiced gleaners of the “truth”, and would deny that their opinions are unfairly skewed by the fact that they are employed by the prosecution. Indeed, they prefer to think of themselves as providing evidence to the Court rather than to the prosecution. The rules of discovery also help to even the playing field; by these rules, the prosecution must share its evidence with the defense prior to a criminal trial, although the converse is not usually required. But the fact remains that while various tests may, themselves, be unbiased and objective, the interpretations of those tests (particularly as regards individualization and reconstruction) can be highly subjective. For example, a test for blood might be viewed as only presumptive by one forensic scientist, but may well be considered proof positive by another. It stands to reason that the opposing attorneys will want to find forensic scientists who happen to hold the opinion most beneficial to their client. For this reason, there are a number of independent forensics labs in the country. However, most of these, based on their past case work, will work only for the prosecution or the defense.

The biggest use of forensic science is at the adjudication (mediation) stage of a case. A witness of Fact or Ordinary/Lay witness at a trial can only offer evidence of things he actually witnessed, and he may neither speculate nor offer an opinion. In contrast, expert witnesses are permitted to offer opinions or interpretation based on training, knowledge or experience in order to help the Court evaluate evidence that the Court lacks expertise with. The opinions are viewed as

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being only those of the witness, and the jury is free to ignore the experts’ opinions. The judge will determine if you are qualified as an expert witness based on the evidence of your qualifications The standard rules for admissibility of scientific evidence court by the expert witness vary from one country to another but generally they are required in those cases in which the matter of inquiry is such that inexperienced persons are unlikely to prove or capable of forming a correct judgment upon it. When the question involved does not lie within the range of common experience or common knowledge, but requires special experience or special knowledge, then the opinions of witnesses skilled in that particular science, art, or trade to which the question relates is admissible in evidence.” In these cases, the prosecution and defense attorneys are allowed to bring various experts before the Court, but all of whom will have to testify that the methods used are broadly accepted by the relevant members of the scientific community. Also, books and scholarly articles constitute compelling proof of a method’s general acceptance, as do prior judicial decisions relating to the technique in question. Courtroom Testimony To testify in a court of law as an expert witness, you will be asked about your “qualifications”. The side for which you are testifying for will ask you to describe your schooling, experience, special training, etc. The prosecution from the other side will then attempt to discredit your qualifications by suggesting that your qualifications are not specific to the case at hand. For example – having training and experience in laboratory sciences does not qualify you to be an expert for in forensic pathology etc. The decision to admit you as an expert is however not up to the opposing side, it is up to the judge’s discretion. Qualifications as an “ expert witness is based on your formal school training , long-term experience in relevant and court case related area, other special training and experience from seminars and personal tutorage In most cases you past experience specific to subject at hand ( i.e. how many similar cases have you examined?) is important . Past publications and presentations and professional recognition and activities in forensic science will further fasten your credibility as expert witness In this regard expert witness might be required to provide CV, list of continuing education and previous legal testimony. Hence it is import to keep a career list of numbers and type of previous examinations, etc you have been involved into.

The Crime Scene investigations I. Review and Overview of Physical Evidence

In a court of law, four types of evidence may be presented: 1) Testimonial Evidence. The evidence comes to court through a witness, who speaks under oath about something he

saw (eyewitness), heard (hearsay witness) or knows (a character witness, for example). 2) Physical Evidence. This represents an object which is real (can literally be taken into the jury room), direct (requires

no preliminary facts) and non-circumstantial (meaning that no inference is required). However, circumstantial evidence is sometimes both offered and strengthened by expert testimony.

3) Documentary Evidence. Samples of writing, sound or video recordings, and transcripts of telephone conversations, for example.

4) Demonstrative Evidence. Types of real evidence used to illustrate, recreate or demonstrate tangible things. For instance, a scale model of a crime scene would fall into this category.

Predominantly, criminalists collect and later analyze physical evidence, although occasionally they may also be involved with documentary or demonstrative evidence, as well. As a practical matter, physical evidence includes any and all relevant materials or objects associated with a crime scene, a victim, a suspect or a witness. Literally, almost any object can be considered a piece of physical evidence under the right circumstances. Physical evidence can be collected at the scene of a crime, on the person of a victim, suspect or witness, or from an area (car, home, job site) associated with a victim, suspect or witness.

There are several different types of physical evidence samples that are likely to be collected and analyzed. A questioned sample (also called an unknown sample) is an object or material which is of unknown origin. It may be lifted from the scene or the victim, for example. One way to establish a connection between questioned sample and a particular person or place is to take a known sample from the relevant person or place for comparison. Known samples can also be called control samples, reference samples and standard samples. Sometimes the known sample has to be produced. For example, a suspect may have to submit several samples of his handwriting. Or a suspect’s gun will have to be fired so as

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to examine both the rifling on the bullets as well as the toolmarks on the cartridge cases. Known samples which are produced are sometimes called exemplars. In processing the crime scene and during the subsequent investigation, it is crucial to remember that one needs to collect both questioned samples and known samples. For example, suppose that at a murder scene there are footprints in moist soil leading both to and away from a corpse. Casts would be made of the shoeprints. Because it is not clear who left the shoeprints, they serve as the questioned samples. If at a later date a suspect is developed, then law enforcement might obtain a warrant to enter the suspect’s home specifically in order to search for and seize his shoes. The soles of the shoes would be inked, and the tread patterns would then be transferred to paper. These transfer patterns would be the known samples. One then proceeds to compare the questioned and known shoeprints, hoping for a match in the tread design and wear patterns. If such a match is discovered, then the questioned shoeprints have been associated, to some level of certainty, with the suspect.

The major goals associated with the analysis of physical evidence include identification, individualization and reconstruction. Individualization is one of the most difficult and yet fruitful aims. Complete individualization is currently possible only for a few types of evidence, including fingerprints, DNA and physical matches (or “jigsaw fits”), but a partial individualization is also often useful. Using the previous example, if the tread design and wear patterns of a questioned shoeprint seem to match those of a known shoeprint, this is a partial individualization. It is not possible to say with 100% certainty that there is a perfect match, because one likely doesn’t know the probability of a random person possessing shoes evidencing such a tread design and exhibiting such wear patterns. Yet the likelihood, while unknown, seems remote to most persons, and juries may find such evidence quite compelling.

Beyond the objectives stated above, the primary goal of analyzing physical evidence is to make the facts of a case clear. The analysis and interpretation of physical evidence can provide several different particular types of information, including: 1) Information on the Corpus Delicti (literally, the “body of the crime”). These facts prove that a crime has taken place.

Examples of such evidence for the crime of burglary would include toolmarks, broken doors and windows, and ransacked rooms. For an assault, pertinent evidence may include the blood of the victim, a weapon, and torn clothing.

2) Information on the Modus Operandi (literally, the “method of operation”, or “MO”). Many career criminals have a characteristic way they commit a particular crime. In burglary cases, the type of tools used and the toolmarks they leave, methods of ingress (entry) and egress (way out) , and types of items taken are all important.

3) Linking a Suspect and a Victim. This is extremely important, particularly in violent crimes. Blood and other body fluids, hairs, fibers and cosmetics can be transferred between victim and perpetrator. For this reason, every victim and every suspect, as well as their clothing and other possessions, must be thoroughly searched for trace evidence.

4) Linking a Person to a Crime Scene. Perpetrators as well as victims may deposit fingerprints, gloveprints, shoeprints, footprints, tire tracks, blood, semen, fibers, hair, bullets, cartridge cases and toolmarks at the scene. Conversely, victims, perpetrators and even witnesses may carry glass, soil, stolen property, blood and fibers away from the scene, and this evidence can be used to prove their presence at the scene.

5) Disproving or Supporting a Suspect’s or Witness’ Testimony. As an example, a person is accused of a hit-and-run accident. Examination of the undercarriage of the car reveals blood and tissue. The owner claims he ran over a dog. A species test on the blood would reveal whether or not it came from a human source.

6) Individualization of a Suspect. Fingerprints and DNA left at the scene are the most conclusive ways of individualizing a suspect. It’s also worth remembering that at many crime scenes leaving a latent fingerprint is perhaps inherently more likely than leaving a locatable DNA sample.

7) Providing Investigative Leads. Physical evidence can be used to productively direct the course of an investigation. For example, a paint chip left at the scene of a hit-and-run can probably be employed to narrow down the number and kinds of possible cars which could have left it.

The overall business of forensic science are usully broken down into the following stages:

• Recognition of physical evidence • Documentation of the crime scene and the evidence • Collection, preservation, inventorying, packaging, transporting and submitting the physical evidence • Analysis • Interpretation • Reporting the results and expert testimony

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Forensic science usually begins at the crime scene, since the bulk of the foregoing pursuits are intimately concerned with evidence retrieved from the actual scene. Thus processing the scene is the first most important events to occur following commission of a crime. If the case is to proceed smoothly through the adjudication stage, the processing must be done thoroughly and correctly. II. Securing, Evaluating and Processing the Crime Scene (this section was not covered in lectures read it The first respondents to a forensic scene are often patrolmen. They will begin by Securing the Crime Scene. In order to accomplish this, the first responder has these responsibilities, in the following order: 1. Initial Response. The primary concerned is safety. Secondary goals include forming a preliminary assessment of the

scene, and beginning to control it. The first responder will: (i). Dispatch and log relevant information (address, time, date, type of call, parties and weapons involved,

etc.). (ii). Beware of any individuals or vehicles trying to leave the scene, writing down (as soon as possible)

descriptions of both fleeing persons (height, weight, race, sex, clothing, etc.) and vehicles (make, model, color, license plate, etc.).

(iii). Cautiously approach and scan the scene, being especially mindful of individuals and vehicles which may be connected to the crime. The first responder should note any potential secondary crime scenes.

(iv). Ensure officer safety before proceeding. One is to assume that a crime is ongoing until he is certain otherwise, and assume that the area is a crime scene until proven otherwise.

2. Safety Procedures. Ensuring the safety of the officers and others in the vicinity of the scene is the principal priority of

the first responder. The first responder will:

(i). Scan the area for sights, sounds and smells which would indicate imminent danger to himself and other responders. He/she also will check for weapons.

(ii). If the scene involves hazardous materials, a clandestine drug laboratory, or chemical, radiological or biological materials, the appropriate personnel or agency ( ie bomb squad, etc.) should be called in prior to the scene being entered.

(iii). After a cautious approach and an initial assessment, all dangerous persons and/or escalating conflicts are controlled and appropriate back-ups are called in. These might include other police, supervisory personnel, etc. The safety of the officer and other parties (victims, witnesses, etc.) is the first priority.

3. Emergency Care. Once dangerous persons and situations are under control, the next priority is to provide medical

attention to injured persons, while minimizing contamination of the crime scene. The first responder will: (i). Assess victims for signs of life and medical needs, call in medical personnel (MP)and, if warranted,

administer first aid. (ii). When medical personnel arrive, the first responder will guide them to the victim in such a way as to

minimize scene contamination. Law enforcement personnel will point out potential physical evidence to the medical personel, instructing them to minimize contact with such evidence. Law enforcement officers should remain with MP, if possible.

(iii). Ensure that the MP’s preserve all clothing and personal effects, and that they do not cut through bullet holes, knife tears, etc., in clothing.

(iv). Document how and to where medical personnel move both persons and items (v). Instruct MP’s not to “clean up” the scene, and to avoid removing or altering items at the scene.

(vi). Obtain names, units and contact information for medical personnel. (vii). If a victim may die, attempt to obtain a dying declaration

(viii). Document statements made by victims, witnesses or suspects. (ix). If a victim or suspect is to be transported to a medical facility, obtain the name and address of the

facility. Send a law enforcement officer along with the victim and/or suspect in order to preserve evidence and document any statements. If that is impossible, request medical personnel to perform the same tasks.

4. Secure and Control Persons at the Scene. To maintain crime scene integrity, safeguard evidence and minimize

contamination, persons found at the scene must be controlled, identified and then separated and removed. The persons who subsequently enter the scene must be thoroughly documented and quite limited in number. The first responder will:

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(i). Control individuals found at the scene, preventing them from moving about, thereby either altering or

destroying potential evidence. (ii). Identify all witnesses, victims and suspects, then separate and secure them. Family and friends of

victims and/or suspects are first identified and then removed from the immediate area. (iii). Exclude all nonessential personnel (law enforcement officers not working the case, media, politicians,

etc.) from the scene.

5. Identify, Establish, Protect and Secure Boundaries. A boundary is established around the scene(s), larger in scope than the scene(s). The rationale is that the boundary can easily be reduced at any later time. But the scene cannot later be easily enlarged since in the ensuing interval it is quite likely that the surrounding areas have been contaminated. The responding officer will:

(i). Establish boundaries of the scene(s), starting at the focal point and radiating outward to include:

• Where the crime appears to have occurred. • Potential points of ingress and egress. • Places where the victim and/or evidence may have been moved from, being mindful of potential trace

and impression evidence. (ii). Set up physical barriers (tape, cones, vehicles, etc.) around the perimeter. Armed guards are employed to

enforce the boundary demarcation. (iii). Establish a single path into and out of the scene, making certain that no physical evidence is distributed

along the pathway (iv). Document and control all persons and animals who enter or leave the scene. (v). Take steps to preserve and protect physical evidence which may be lost or compromised. For example,

evidence should be protected from rain, snow, and so forth, as well as from sprinklers, footsteps, etc. (vi). Document the original locations of persons or objects which were seen to have been moved.

(vii). Consider search and seizure issues to determine the necessity of obtaining either a consent to search and/or a search warrant.

(viii). Ensure that persons at the scene (including law enforcement personnel) do not alter the scene in any way. Thus, smoking, eating and drinking are not permitted. One may touch nothing. Hence, windows, doors, thermostats and so forth are left exactly as they were. Responders cannot leave litter or other debris.

6. Turn Over Control of the Scene and Brief the Investigator in Charge. At some point a lead investigator (or detective)

will be assigned to the case. The first responder will: (i). Brief the lead investigator, providing a synopsis of the incident so far.

(ii). Show him the scene boundaries and the chosen path in and out of the scene. (iii). Turn over responsibility for documenting personnel entering and exiting the scene to the lead

investigator. (iv). Remain at the scene until formally relieved, being sure to document his own departure time.

7. Document Actions and Observations. As soon as possible, the first responder should clearly and concisely document all his actions and observations at the scene. This is absolutely essential for preserving information which otherwise will be forgotten, and for providing information which may substantiate or contradict later investigative leads and theories. The documentation must be permanently preserved as a part of the case record. The first responder will:

(i). Document the state of the scene upon his arrival, including the location, condition and appearance of

people and objects. (ii). Document existing conditions upon arrival. For example, were the lights on or off? Were doors and windows

closed, ajar or fully open? Was any furniture moved or overturned? What was the temperature and what were the weather conditions? Were any unusual materials or odors present? Was there any deteriorating evidence (such as tire tracks in melting snow)? Were appliances on or off? Were motor vehicles on or off? If off, was the engine warm or cold?

(iii). Document all personal information concerning witnesses, victims and suspects, and record their actions and statements.

(iv). Record the actions of himself as well as of other law enforcement and medical personnel. Record all personnel who entered (and exited) the scene, their actions at the scene, and any items which may have been moved, and by whom.

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In Summary (a) From a forensic science viewpoint, the foregoing procedures are absolutely essential as there are many steps in to e

followed which ensure that physical evidence is not lost, contaminated, or moved. That is, the physical evidence which may be present is preserved for later identification, collection and submission. Included here are things like demarcating the scene, and then being very selective about who is able to enter and leave it. The establishment of a single path into and out of the scene, and subsequent insistence that all personnel use this pathway, also preserves physical evidence. If the evidence must be moved, or is moved inadvertently, its original location is documented. This might be important if a reconstruction is to be attempted later. By documenting all personnel at the scene, one is anticipating not only the necessity of investigators later needing to interview these persons, but also anticipating the need of obtaining known samples (of fingerprints, hairs or shoeprints, for example) from them at a later time. Also by documenting all the persons who entered and left the scene, and whether or not they touched or moved any objects, one is establishing and safeguarding the chain of custody.

(b) From a legal standpoint, one of the more interesting aspects of the foregoing procedures is the attempt to get a dying declaration from a victim who may expire. This is because a dying declaration is one of the several exceptions to the “Hearsay Rule”. Hearsay is second-hand evidence. In many instances, hearsay is not admissible evidence in a court of law. The common law in the US recognized five exceptions to the Hearsay Rule. A dying declaration is one of those five historical exceptions. So if a victim utters “John Mdoe killed me!” and then expires, that dying declaration will be admissible evidence, even though the victim/witness has since died and cannot be cross-examined by the opposing side.

(c) From an investigative viewpoint, it is important that all victims, suspects and witnesses be identified and then

separated. The police will later want to interview these people separately to see how their various stories may agree or diverge. By separating them early on they are given less opportunity to “get their stories straight”.

Once a lead investigator is called to the scene it is his responsibility to direct the investigation. His first task will be to Evaluate the Scene, particularly in order to establish whether or not the scene should be processed for physical evidence. Not all scenes will lend themselves to an identification and collection of physical evidence. And the very costly nature of collection and analysis may cause some jurisdictions to collect physical evidence only in instances of crimes of a more serious nature. If the decision is made to process to the scene for collection of physical evidence, then the lead investigator will direct and control the processing. The scene evaluation will generally proceed as follows.

1. Conduct Scene Assessment. The lead investigator will be briefed by the first responder. He will evaluate whether or

not the preliminary steps outlined above have been accomplished and, if not, he will take corrective measures. Included would be a review (and possible modification) of things like scene demarcation; path in and out of the scene; search and seizure issues; identification, containment and isolation of victims, witnesses and suspects; and so on. In addition, the lead investigator will:

(i). Determine whether or not a prosecutor or other specialized legal personnel should be called to the

scene. (ii). Establish a staging area for consultation and equipment. Of course, such an area should be near the

scene but not be a part of it. (iii). Establish a secure area for temporary evidence storage, being mindful of environmental factors which

could degrade the evidence, as well as being cognizant of the chain of custody (which we will talk about later). The area is secured by armed personnel.

(iv). Canvass the surrounding area looking for additional evidence, secondary crime scenes, and witnesses. (v). Arrange for the immediate photographing of all victims, suspects and witnesses still at the scene,

especially showing any injuries (or lack thereof). Additionally, the lead investigator will arrange for the photographing of any evidence or conditions which may be subject to imminent degradation or change.

2. Crime Scene “Walk-Through” and Initial Documentation. The lead investigator will do a quick walk-through of the

area, probably accompanied by the responding patrolman, gaining an overview of the situation. If possible, other personnel who will later be responsible for documenting and processing the scene will also participate in the walk-through. The goals are to:

(i). Develop a preliminary plan for a more detailed search and documentation of the scene.

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(ii). Note the placement of obvious pieces of evidence. (iii). Document the scene as it currently appears by making notes, taking preliminary photographs, making

rough sketches, etc. (iv). Identify, document and collect any fragile or degradable evidence. At this point the major Processing of the scene is ready to commence. This is the point where physical evidence is first recognized (although, in fact, this may have happened already for some pieces of evidence) and then documented. In some ways, this is where forensic science begins. However, one cannot underestimated the importance of the previous tasks, as performed by the first responders. If the responding officer doesn’t properly secure the scene and preserve evidence, no amount of forensics can save the case. The steps involved in processing are as follows.

3. Determine Team Composition. The lead investigator makes certain that personnel sufficient in both number and expertise are available for processing the scene, and that each individual is aware of his particular responsibilities. The lead investigator will:

(i). Assess the need for additional law enforcement and/or investigative personnel, especially in light of

potential multiple scenes and/or multiple jurisdictions, multiple victims, and/or the existence of numerous witnesses.

(ii). Assess the need for additional equipment (lighting, ladders, etc.). (iii). Evaluate the need for specialized law enforcement personnel (CIDs) and medical personnel. (iv). Determine if their is a need for specialized forensic personnel and/or equipment is warranted, paying

particular attention to specialized evidence collection needs (fingerprint specialist, firearms expert, blood stains and spatter expert, trace evidence specialist, arson investigator, and so forth).

(v). Selected qualified personnel for specialized tasks, including special photography needs (underwater, aerial, etc.) and special sketching needs.

(vi). Assign specific and specialized tasks to particular personnel, establish relative priorities, and document all assignments. He will follow up to make sure that each assignment is being carried through.

4. Ensure Contamination Control. As evidence is identified, documented and later collected, several dangers present

themselves. First, the investigators may inadvertently contaminate the evidence, perhaps by moving it, stepping on it, or even by depositing new material on top of it. Second, as swabs and other devices are removed from their packaging, there is a danger that investigators will leave the packaging at the scene, thereby contaminating it. Third, collecting biological samples potentially puts the investigator or technician at risk of contracting diseases such as AIDs and hepatitis. Finally, if a lot of evidence will be collected there is the danger of cross-contamination between different pieces of evidence. To alleviate these concerns the lead investigator will:

(i). Continue to make certain that nonessential personnel are not permitted within the boundary demarcating the

scene, and continue to make certain that essential personnel follow the prescribed path into and out of the scene.

(ii). Consider collecting elimination samples from first responders, medical personnel, investigators and technicians. Elimination samples are known samples (of fingerprints, shoeprints, hairs and so on) taken from law enforcement and medical personnel who may inadvertently leave such evidence at the scene. Later, if a questioned sample can be shown to trace back to such personnel, the questioned sample is considered to have been individualized to legitimate crime scene personnel, and it need not be considered further as a source of meaningful criminal evidence.

(iii). Designate an area well outside the scene for trash and equipment storage, and assign responsibility for trash and equipment removal.

(iv). Assess potential biological hazards, and ensure that the appropriate Personal Protective Equipment (PPE) is being employed by essential personnel. The PPE must later be properly disposed of in a biohazards container.

(v). Make sure all equipment starts clean and (if appropriate) new. Reusable equipment must be re-cleaned after each use and again prior to storage.

(vi). Single-use equipment (scalpels, pipets, swabs, gloves, etc.) must be used for all biological evidence, and perhaps for some other types of evidence, as well. All single-use equipment must be disposed of properly (e.g.: into a “sharps” container) after a single use.

At this stage, the scene is ready to be Documented, meaning photographed, video (and perhaps also audio) taped, measured and sketched. All this must be accompanied by the taking of copious notes. More than

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anything else, the focus is on documenting the physical evidence found at the scene. Because the various components of documentation are so forensically important, each will now be discussed in some detail.

III. Recognition of Physical Evidence From the forensic science perspective, the first step in processing the scene is the recognition of the gross (or obvious) pieces of physical evidence. Actually, this process starts almost as soon as the first responder appears on the scene, and is an ongoing task throughout the early stages of the investigation. By the time the scene is ready to be processed, many of the more obvious pieces of physical evidence will have been discovered. Many more pieces may be unearthed later, but one must at least recognize the major items at the outset so that they can be documented.

This recognition is largely a matter of experience. On the one hand, if every object which is simply present at the scene is documented, collected and sent for analysis, the result would be overwhelming, immobilizing and chaotic. On the other hand, if important evidence is not collected, the case might never be prosecuted successfully.

As early as his walk-through, the lead investigator will probably start imagining several scenarios whereby the crime may have been committed. Then he will focus on what sorts of physical evidence would be expected under each of these scenarios. Evidence is then selected in order to validate, refute or distinguish among these several possibilities. In order for this to be meaningful the lead investigator must be aware of what information later analyses might be expected to reveal, particularly recalling the individualization and reconstruction goals of the forensic scientist. It is not always possible to precisely reconstruct a crime, and it is not always feasible to completely individualize a sample, but in both instances it is almost always possible to limit the possibilities. To cite an example, suppose two bodies are discovered, each with a single bullet wound. Also suppose that a firearm is resting very near one of the bodies. Is this a double murder, a double suicide, or a murder-suicide? The lead investigator will focus on looking for evidence which would indicate one or the other of these, and also evidence which would distinguish one from the other. Thus, he may direct that the hands of each corpse be swabbed to test for gunpowder residue. If both corpse’s hands have such residue, the double-suicide theory is indicated. If one corpse’s hands evidence residue, but the other’s are clean, then the evidence points to murder-suicide. The absence of any such residue would lend support to the double murder scenario.

Also, the investigator must know what type of physical evidence is required to successfully prosecute a particular case. As was noted before, for instance, a charge of rape can generally be sustained only if evidence of penetration is found in the lab. In short, there is no substitute for patience, knowledge and selectivity.

Because recognition of physical evidence is an art form, many police departments employ specialized evidence retrieval technicians. We have previously noted that the FBI maintains ERT’s, and the GBI has its own equivalent CSS’s. However, in most cases these specialized units must be called in by the local authorities. As mentioned previously, it is far more common that the police on the scene are responsible for evidence recognition, documentation and collection, although many larger departments do have specialized evidence retrieval technicians. Here again it is important to recall that no amount of later forensic analysis can overcome mistakes made by these individuals at the scene. IV. Documenting the Scene and the Evidence

Documentation is crucial from both legal and scientific standpoints. From the legal perspective, maintaining the chain of custody will demand that nothing be altered prior to its being documented. If items have been moved, either out of exigency or inadvertently, then it is necessary that their original location, as well as the circumstances which led to their having been moved, be documented. Also, the chain of custody will require documenting who discovered an item of evidence, when it was discovered, its appearance, and who took control of it.

Even in a case where a suspect has been arrested and confessed, the documentation step cannot be skipped. In just such cases an attorney may later claim that investigators unfairly focused on his client, that the confession was coerced, that other suspects could have been identified from the evidence at the scene had it only been processed, that lack of documentation is a reflection of generally inadequate or unfair investigative techniques, etc. In short, there is no such thing as an open-and-shut case in the early stages. Further, documentation will be required for presentation at trial in order to describe the crime scene and the location and condition of physical evidence retrieved form it.

From a scientific standpoint, documentation later helps the analyst understand the relation of the evidence to the overall scene, and may suggest what types of analyses to perform on the evidence.

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As was mentioned previously, the lead investigator should have already developed several hypotheses about what may have occurred. The investigator or evidence technician then goes about documenting what facts tend to corroborate, refute and distinguish among these various hypotheses. The investigator or technician will also have to anticipate various questions that may arise later and be willing to look for evidence which bears on the answers to these questions. The working hypotheses may well have to be modified as time goes on, but they at least allow for order to develop out of what otherwise might be chaos. Thus, the lead investigator or evidence technician is as much an interpreter as he is an observer and recorder.

As mentioned above, several different means of documentation are available including notes, sketches, photographs, and audio and video recording. These are mutually complementary and should all be used in most circumstances.

Notes

These constitute the core of the crime scene and physical evidence documentation. They must be made in ink in a bound notebook, the pages of which have been previously numbered sequentially. Errors should never be corrected by erasure or by removal of pages, but by marking through the errors with a pen followed by entry of the corrected information. Likewise, no blank spaces should be left for observations or conclusions to be inserted later. All notations must be recorded in a strictly chronological order. All these requirements help to avoid later allegations of tampering or “fudging”.

Note-taking must be a constant and ongoing activity. It starts with the first responding officer, who must log such issues as time and place of arrival, appearance of the scene, names and addresses of persons present, and so on. Even medical personnel must keep logs of their activities at the scene. The notes will document the location and overall appearance of the scene. Any transient evidence (sounds, smells, etc.) will be mentioned, as will any departures from usual procedures.

All evidence which is observed must be documented in the notes. Its condition, time of discovery, name of discoverer, placement, collection, packaging and labeling must be described, as must its eventual disposition. This may be done is a separate evidence log. Further, every photograph which is taken must be documented in the notes, including roll and frame numbers, date, time, subject matter, location, camera settings, specialized lighting or film, etc. Sometimes such information is included in a separate photography log. The notes are the principal way of jogging one’s memory months or years later, and must by sufficiently detailed for this purpose. Additionally, the notes must document and prove the chain of custody.

It is possible to use an audio recorder as an adjunct to written notes if available. Alternatively, one may simply narrate during videotaping. The advantage is that a lot of detail can be included without the cumbersome task of having to write it all down at the moment. However, soon after leaving the crime scene the audio notes must be transcribed and then stitched together with the original written notes to produce a new and complete set of written notes. It is essential the both the original written notes and the audio tape be preserved as evidence.

It is the written notes that tie together the other forms of documentation. During subsequent hours, days and weeks the notes may reflect changes in the working hypotheses, a narrowing of the focus to a single hypothesis, additional forensic observations, and finally a theory of the crime.

Sketches The purpose of sketches is to accurately record the spatial relationships among salient objects at the scene. Significant dimensions must be accurately determined with a tape measure and incorporated into the sketches. The sketches produced at the scene are known as rough (or preliminary) sketches. They need not be accurately drawn nor to scale, but they must contain all the information necessary to allow an accurate rendering later on. In particular, the sketch must evince

(i). A case identifier (ii). Date, time and location

(iii). Weather and lighting conditions (iv). Identity and assignments of personnel (v). Dimensions and layout of rooms, furniture, doors, windows, skid marks, etc.

(vi). Measurements showing location of evidence; each object should be located by two measurements from immovable objects such as doors, walls, corners, mile posts and other road signs, manhole covers, other

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fixed landmarks, etc. In this way, triangulation can later be used to accurately fix the position of every salient object.

(vii). Key or legend (identifying objects which are given alphanumeric designations in the actual sketch), compass orientation, and a scale (or a scale disclaimer)

Taking photographs does not alleviate the need to make sketches. First, photographs produce a false sense of perspective and do not ordinarily allow for accurate dimensions and spatial relationships to be determined later. Another advantage of sketches over photography is that they permit the emphasizing of the most relevant objects and features and allow for omission of the remainder. On the other hand, a photograph will include all objects present, whether they are pertinent or not.

Much later, especially as the adjudication stage nears, a professional will prepare finished sketches based on the information contained in the rough sketches. The finished sketches will be suitable for courtroom presentation. In the most elaborate instances, the computer program are available can be used which allow one to zero in on certain rooms or areas, with icons representing bodies, firearms, blood spatters, and so on. At trial the sketches can either be blown up and printed for viewing by the judge and jury, or the entire file can be loaded on a computer and projected for viewing in the courtroom.

Photographs

Photography, particularly with a 35 mm camera, is unsurpassed in recording vast amounts of intricate detail. Unfortunately, photography is often underutilized (probably because it has the unfounded reputation of being relatively expensive) or misused (because of inadequate training of personnel). Aerial shots can succinctly summarize the entire scene in a most comprehensive manner. • Long shots depict the area(s) where the crime occurred, as well as surrounding areas, points of ingress and egress,

etc. • Medium shots show the gross location of evidentiary items and their relationship to one another and to the entire

scene. In addition, if the crime was indoors, all walls, ceilings and floors of the room and of any adjacent rooms are photographed. If a body is present, it is photographed from medium range to show its relationship to other elements. Once the body is removed, the area under it is photographed. Medium-range shots are taken of things like crowds and vehicles, also. It is also wise to take photographs from different angles and perspectives. For instance, medium-range photos are taken from the victim’s viewpoint, and then from a witness’ viewpoint, etc.

• Close-ups are used to provide details of each object of evidence, including wounds, weapons, cartridges, etc. Close-ups are also taken of each victim, suspect and witness. Close-ups should contain at least one scale (use a measurable tape, ruler) , and preferable two scales held at right angles to one another, and also should show an evidence identifier.The scale(s) establish the proper dimension(s) of the object later. Afterward, the same evidence is often re-photographed without the scale(s) and identifiers. It may be necessary to take several shots of the same object under different lighting conditions and perhaps even using different film types.

Digital cameras, while expensive, also show immediate results. They also possess the additional advantage that several still shots can be stitched together electronically to form a 3-D panoramic view of the scene. However, the resolution of digital cameras is not as good as analog 35 mm cameras, and the digital image is much easier to manipulate. This can lead to charges of tampering. Thus digital cameras may become increasingly used to augment analog cameras, but it is doubtful they will replace them entirely, at least in the immediate future.

Photographs must be taken while the scene is pristine (untouched). Unless injured parties must first be moved, all items must be in their original, undisturbed states in the photos. If items are removed or added, or if their spatial relationships have been otherwise altered, the photos may not be admissible evidence. If it happens that evidence has been moved prior to taking a photo, that fact must be mentioned in the notes. It is not permissible to later reintroduce or shift any previously moved or altered objects for purposes of taking a picture.

Just as audio recording can be used as an adjunct to written notes, video recording may be used to complement still photography. A video is perhaps the best way to document the overall, gross record of the scene; it gives a good picture of the “lay of the land” and aids in understanding the relationships of various pieces of evidence to each other and to the scene. The video camera is also a superb method of documenting the investigation and evidence collection process, and provides a very convenient way of documenting the sequence and locations of the still photos. As an added benefit, the audio track can simultaneously record a running narrative. Finally, forensic scientists (who frequently are not present at the scene) often find a video allows them to understand the scene very well at a later time. But it is important to remember that the resolution of a videotape is considerably poorer than that of 35 mm film, so the former can never replace the latter as a means of recording detail.

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V. Systematic Search for Evidence Obvious pieces of physical evidence are documented at the outset of the investigation. Subsequently the entire scene must be methodically searched in order to glean less obvious but pertinent pieces of physical evidence. It will be the lead investigator who coordinates the search. The question of how to search, while important, is perhaps secondary to the issue of what is being searched for.

The scene is searched by employing a search pattern. Common patterns recommended is • Spiral (or Concentric) (either from inside-out or outside-in) • Grid (go N-S first, then E-W, for example) • Strip (or Line) (N-S or E-W only, for example) • Zone (or Quadrant) (one searcher per several equal-size areas) The suspected points of ingress and egress must also be searched.

Regardless of which search pattern may be selected, the search must be prioritized. Safety, weather, security and traffic may dictate that some areas be searched first while others can wait. In the same way, evidence which is transient or fragile will have to be collected first, being cautious to not disturb other evidence which may be nearby. If chemical agents (such as fingerprint powder or luminol) are to be used, certain other evidence (which might be contaminated by the chemical agents) must be collected first. Finally, the lead investigator must be cognizant of the need to employ special techniques (alternative lighting, chemical enhancement of stains, etc.) and highly trained personnel (blood spatter analysts, projectile trajectory analysts, etc.), and that these techniques and personnel may further restrict the order in which evidence is documented and collected.

VI. Collect, Preserve, Inventory, Package, Transport and Submit the Physical Evidence (CPIPTP)

Once evidence is located and its discoverer, time of discovery, location and appearance have been thoroughly documented, then it is time to collect and preserve the evidence, inventory it, and then package it in preparation for sending it to the crime lab. Exactly how this is accomplished depends on the type of evidence.

Impression evidence (tire tracks, footprints, toolmarks, latent fingerprint, palmprints, and so forth) is often developed or enhanced by use of specialized photographic techniques (alternative light sources and filters) and/or by application of chemical developers (fingerprint powder, ninhydrin, silver nitrate, etc.). Collection may be accomplished by photography, physical lifting (as with tape for fingerprints, gel lifters for bite marks, molding materials for tire impressions, etc.), or by actually taking the entire item upon which the evidence has been deposited.

Biological evidence will often be located visually, and sometimes will have to be enhanced and/or developed via chemical means (luminol, presumptive tests for blood, semen, etc.). Single-use equipment (swabs and gauze) can be used to sample stains. Alternatively, dried stains can be scraped (with a scalpel, perhaps). The entire item evidencing the stain (clothing, door, etc.) can be taken, or a portion of the staining can simply be cut out of the object using a scalpel.

Arson, explosion and bomb evidence is located visually and also by smell. Ignitable liquids are removed with shovels. Burned materials (or portions thereof) are removed from the suspected point of origin of the blaze or blast. Ignition devices, fuses and exploded bomb components are simply taken in toto.

Trace evidence is collected by manual means (forceps, tweezers, gloved hand), scraping, taping and/or vacuuming. As a last resort, the entire item containing the evidence can be removed.

Chemicals and controlled substances are located by visual observation (drug , pipes, etc.), by use of field (or presumptive) tests, by drug detecting animals, and by odor. The items are generally removed in their entirety.

It must be recognized that some evidence is microscopic and cannot be detected visually by personnel at the scene. Minute droplets of blood on clothing is an example. Thus, likely carriers of such evidence (such as the clothing of all

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victims and suspects) must be collected. Also, the undersides of all fingernails should be scraped using a toothpick or other dull instrument for possible blood and tissue evidence. When feasible, areas of the crime scene should be vacuumed and the collected evidence submitted for hair and fiber analysis; different areas are vacuumed separately and the debris collected is likewise submitted separately.

It is during this stage that one must be very mindful to not only document and collect questioned samples but also known samples and elimination samples. For instance, if a victim is found to have soil on his clothing, it should be sampled. However, at the same time it is essential to take several known soil samples from various areas of the scene. Similarly, if blood spatters are discovered they will be sampled. It is just as important that a known sample be taken from the victim and, perhaps later, from any suspects. If DNA analysis is to be performed on questioned blood or semen, it is generally sufficient to use a buccal swab to obtain a known sample of the DNA of the victim or suspect. Finally, hair and fiber samples from victims and suspects must be taken for later comparison with questioned hairs and fibers that may have been retrieved via vacuuming the scene. All this points there must be a very close cooperation between all investigators. If a victim is autopsied, the Medical expert (ME) will automatically collect organ and tissue samples for pathological and/or forensic analysis into the cause of death. In addition, blood samples will be taken, especially for running toxicology scans. Investigators will have to be in contact with the ME to obtain samples of

• Clothing • Fingernail scrapings • Head and pubic hairs • Blood • Vaginal, anal and oral swabs (for sex crimes) • Bullets from the body • Hand swabs from shooting victims (for gunshot residue)

It is, of course, considerably more difficult to obtain all these samples once the body has been buried. Additionally, as time progresses defense attorneys can argue that the original evidence has become tainted or otherwise altered over time Substrate control samples It is also imperative to document and take substrate controls when sampling some types of evidence. Suppose there is a blood droplet on a piece of clothing. The questioned blood is sampled. But other unstained areas of the clothing should also be sampled; these are the substrate controls. In the lab it will be necessary to prove that the questioned sample tests positive for the presence of human blood. But it will be just as important to show that the substrate controls all test negative for the existence of human blood, thereby indicating that the positive test derived from the questioned sample was not a “false positive” somehow induced by the properties of the cloth (or substrate) upon which the blood droplet was deposited.

One must also be mindful to collect electronically recorded evidence from the scene or the general vicinity of the scene if this is possible. Answering machine tapes, voice mail messages, computers, cell phones, fax machines and the videotapes from nearby surveillance cameras all may contain important clues and should be documented and taken.

Evidence of substantial size should be marked directly with the case identifier, the collector’s name (or initials), time and date, and other salient features. Often all evidence collected is described in an evidence log, wherein it is given a unique identifier (e.g.: ... 14. Rectal swab from victim. 15. Vaginal swab from victim. 16. Mouth swab from victim...). It is then packaged; the same sorts of information used to mark the sample should also be used to mark the packaging. For smaller samples (such as trace evidence), the sample itself cannot be marked. Therefore a sketch and description should be entered into the notes or evidence log, and then the sample is packaged; the pertinent information is simply recorded on the package itself rather than directly on the evidence. All these details must be described in the notes.

The type of packaging depends on the evidence itself. The primary goals are protection of the evidence and preservation of its integrity. One must particularly prevent breakage, damage, evaporation, loss and cross-contamination. Screw-cap glass vials, plastic pill bottles, and manilla envelopes can all be used for a variety objects such as paint chips, glass fragments, soil samples, hairs, fibers, powders, etc. For liquid samples it is crucial that evaporation be retarded. For small samples, screw-cap glass bottles are satisfactory. For larger samples (such as charred wood suspected of containing traces of an accelerant, like might be collected from an arson scene), the sample can be put into a new one- or five-gallon paint can and then sealed. Clothing can be put into large paper sacks.

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Blood is of special concern because it so commonly found at crime scenes and because its improper handling can be disastrous. If moist blood is placed in an airtight container, mold and mildew may grow, and this taints the evidentiary value of the sample. If the blood is wet it can be swabbed and then the swab permitted to dry. The swab can then be placed in a manilla envelope. Alternatively, the blood can be allowed to air dry. Dried blood is usually sampled by scraping; it may then be put into a manilla envelope. Wet clothing (whether the moisture is due to blood or otherwise) is treated similarly, excepting that it is usually placed into large paper sacks. No folding of clothing is usually permitted, as this may potentially cause cross-transfer of trace evidence from one area of the garment to another.

Generally, it is often best to take samples in their native condition. For example, bloodstains, semen stains and soil stains on a garment may not be swabbed or scraped; instead, the whole garment could be dried and then submitted. In this way, other trace evidence which may be present will also be available for the forensic examiner. There are many instances where significant portions of structures (doors and pieces of drywall and floor, for example) are removed and sent in their entirety to the lab. And it is very common that an entire car will be submitted, especially in cases of hit-and-run, homicide, etc. For many types of evidence, only if the questioned sample is adhering to an impossibly large structure will it be removed (with forceps or other appropriate tools) and submitted separately from the structure on which it was found.

As evidence is collected at the scene, it is removed and store temporarily in a separate, secured evidence collection area, which is constantly guarded. Once all the evidence is collected, it is ready to be transported and submitted to the crime lab or to an evidence storage area maintained by the police.

Evidence may be submitted to the crime lab either via mail or by personal delivery. The latter method is usually chosen if the case is urgent and if the laboratory is not too far away. It should be noted that various mail and parcel carriers have special regulations that may apply to evidence from a crime scene. Etiological agents (viable microorganisms and their associated toxins, which can cause disease in humans) should be shipped in specially marked and constructed containers via registered mail.

Laboratories will require that an evidence submission form accompany all shipments. Included will be such obvious things as the submitter’s name and a case number, a list of the items sent as well as a unique alphanumeric identifier for each, what analyses are requested for each, and a brief case history. The items themselves are packed separately. The criminalist may well need to perform analyses is addition to the ones requested, especially in light of new developments in the case or as a result of previous tests. On the other hand, the analyst may decide that the requested examinations are impossible or unlikely to be beneficial. In short, the analyst is not bound by the submitter’s requests for particular examinations.

VII. Chain of Custody

At the adjudication stage, all evidence will be subject to questions regarding the maintenance of the chain of custody. This refers to the prosecution’s need to completely account for the discovery, collection, analysis, storage and transfer of the evidence during the entire time between its original finding during the crime scene processing through adjudication (negotiations/settlements) , and even through possible subsequent appeals.

The chain of custody starts with the original discoverer. This is one of several major reasons why evidence must not be moved prior to its documentation and retrieval. If the evidence is moved prior to its documentation, and if all the facts surrounding that movement are not documented completely in the notes, than the chain of custody has been broken, potentially rendering the evidence tainted, even useless. The chain of custody is also part of the reason why, when possible, evidence is sent in “large chunks” with identifying marks (such as the collector’s name or initials, date, and description) directly on it, rather than by cutting out or removing smaller portions which cannot be labeled individually. The case identifier and other pertinent information listed on packaging materials holding the evidence provides yet another means of trying to document the chain of custody. In the end, one of the most important ways the chain is preserved is by making certain the notes completely document everything that happens to each piece of evidence at the scene, all the way from its discovery to the point where it is sent to the lab.

Some jurisdictions have developed special chain of custody forms which accompany each piece of evidence. The form shows who received the item, and when, and to whom they relinquished it, and when.

The chain continues when the evidence is shipped to the crime lab. The evidence submission form is an integral part of the chain, describing the items sent and identifiers for each object.

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Failure at any stage to properly document who has possession of the evidence and what they did with it (and when) can lead to the tainting of the evidence and its exclusion from a subsequent trial. Because every person who has handled the evidence must be able to show an unbroken chain of custody, it is wise to keep the number of such persons to an absolute minimum.

Physical Evidence Analysis, Interpretation and Reporting

In the preceeding sections we defined physical evidence as any and all relevant materials or objects associated with a crime. Such evidence is real, direct and non-circumstantial. Physical evidence can be collected at the scene of a crime, on the person of a victim, suspect or witness, or from an area (car, home, job site, etc.) associated with a victim, suspect or witness. Additionally, we broke the overall business of forensic science down into the following six stages: • Recognition of physical evidence • Documentation of the crime scene and the evidence • Collection, preservation, inventorying, packaging, transporting and submitting the physical evidence • Analysis • Interpretation • Reporting the results and expert testimony We addressed the first three of these activities previously. In this section we focus on the remaining three aspects, all of which intimately involve criminalists. Classification of Physical Evidence Evidences arrives at a crime lab either by mail or hand delivery. In either case, an evidence submission form should accompany the evidence. This form should describe the crime which occurred, the individual pieces being submitted, and what analyses are requested for each. The evidence submission form is an important element in the chain of custody.

One advantage to the hand delivery method is that the criminalists can ask the delivering officer intimate questions associated with the investigation of the scene and case. This can help to suggest a different analytic approach than that requested on the original evidence submission form. In any case the criminalist is not bound to analyze the evidence in the manner requested on the form if he feels another approach would be more enlightening or if he feels the original request is impossible or unlikely to be of value.

From the analyst’s point of view, perhaps the best way to begin analysing the evidence would be to try to classify the evidence one is presented with. There are a number of possible classification schemes, no one of which is best under all circumstances and each of which may be useful at times. Included would be classification according to the • Type of Crime • Type of Material • General Nature of the Evidence • Physical State of the Evidence • Type of Question to be Resolved • Way the Evidence was Produced • Appropriate Laboratory Approach Classification by the Type of Crime Here one would think of there being homicide evidence, rape evidence, burglary evidence, and so forth. This can be useful as a way of reminding an investigator to be sure to check for certain items at a particular kind of scene. For example, in a homicide one would be certain to check for blood, firearms, ammunition and cartridges, other weapons, fibers, hairs, etc. The problem with this approach is that it is self-limiting. Almost any kind of evidence can be an element of almost any crime. Blood evidence, e.g. can be associated with assault, rape and burglary almost as frequently as it can be with homicide, and semen evidence, which is important in a rape case, may just as well be present at a homicide scene. While there is some correlation between the type of crime and the type of evidence, the correlation is usually imperfect and should not be relied upon too heavily. Unexpected and unpredictable pieces of evidence might be quite important in solving a particular case; yet these sorts of things would be most likely overlooked by someone who simply memorized a “checklist” to go through for the particular type of crime which occurred.

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Classification by the Type of Material In this case there would be paint, plastic, wood, glass, metallic evidence and so forth. This is not often a useful classification scheme. For example, a questioned plastic bag might be tied to other plastic bags in the suspect’s possession by matching striation marks present in the bags themselves. However, this type of comparison is basically the same process one would follow if one were to compare a part of a wooden ax handle left at the scene with a fragment of an ax handle found in a suspect’s possession. The important thing is the “fit” of the surfaces and not the fact that one is dealing with wood or plastic. Another shortcoming of this method is that quite commonly the important information is not what the material is but, rather, how it may have interacted with other objects. For example, for some plastic bags it is the striation marks which are important. In other cases it may be a fingerprint on the bag which is crucial, and this eventuality has less to do with the bag, itself, than it does with interaction of the bag with a person.

Classification by the General Nature of the Evidence Here we are referring to typing things as being chemical, physical or biological. Physical evidence might include firearms, cartridge casings, tools and toolmarks, fibers, documents, glass and soil etc. Chemical samples would be those things which have evidential value based mainly on their chemical properties or structures. Included would be drugs, explosives and residues, arson accelerants, solvents, petroleum products, etc. Biological specimens would include hairs, blood, urine, semen, saliva, organs, and so on. Generally, this scheme is too broad to be very useful except that it might remind investigators and criminalists that special precautions are frequently required to preserve samples in the “biological” and “chemical” categories. Classification by Physical State of the Evidence This mean thinking of samples as being in the solid, liquid or gaseous state. The great majority of physical evidence is usually in the solid state; i.e. clothing, fibers, hairs, glass and weapons, as well as dried biologicals (blood, saliva, semen, etc.). Thus the “solid” category is too broad to be very meaningful. Liquids are rarer; examples include solvents at illicit drug labs, and fresh biologicals. The principal benefit of classifying some materials as “liquids” would be to remind investigators and analysts that liquids may evaporate unless properly sealed. Remember that bodily fluids which are present in “wet” form must be permitted to dry thoroughly before they are packaged. Finally, there is little physical evidence ever submitted in the gaseous state. Classification by the Type of Question to be Resolved Here one thinks of evidence in terms of whether it will eventually be used to:

• Prove an element of a crime (such as the presence of penetration in a rape case) • Link a suspect to a victim, or a person to the scene. Included would be all manner of cross-transfer evidence such

as hairs, fibers, soil, body fluids, etc. • Exonerate or cast suspicion on a suspect, or corroborate or disprove an alibi or a witness’ statements. • Aid in reconstruction. Examples include determining the trajectory of a bullet or the position of a shooter

relative to a victim, etc. • Provide investigative assistance in developing leads. • Be eventually used in a court of law.

These ways of thinking about evidence are extremely useful in the investigative stage. It is likely that the lead investigator will be thinking in just such terms as he does his preliminary walk-through of a scene and then plans for a thorough documentation, search and retrieval of evidence from the scene. Classification According to the Way the Evidence was Produced The important consideration here is how does the evidence reflect the act being investigated, how would such an act cause various object to interact with one another, and how would the various objects be mutually affected by such interactions. The physical evidence presents one with a record of interactions which, if properly decoded, can be quite illuminating. Several subclasses of interactions are conceivable. 5. Position and/or Geometric. The position and/or apparent movement of objects is recorded as an aid in later

reconstructions. For example, if a wounded person is running and simultaneously dripping blood, the patterns of the blood spatters on the floor will prove in which way the person was moving at any given moment. If the wounded person is being chased, the pursuer will inadvertently step in some of the blood drops, smearing them and probably leaving shoeprint fragments in many different places. If the shoeprints can be individualized back to a suspect, then one has proven that the suspect was chasing the wounded victim, and one can also map out how that chase proceeded.

6. Imprints and Indentations. Items here would include fingerprints, palmprints, shoeprints, tire tracks, cloth impressions, bite marks and toolmarks (pry marks, primer marks on cartridges, etc.). Individualization is the ultimate

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goal, with the questioned imprint or indentation being compared to an exemplar made by the interaction of an appropriate known object associated with a suspect in (or on) a similar medium.

7. Striations. These are marks produced on surfaces when such surfaces are in contact sliding motion relative to one another. It is this motion which distinguishes striations from imprints and indentations, both of which are left by a more static contact between surfaces. A toolmark left by a sliding of the tool across a surface is an example, as are the striations left in a plastic bag due the extrusion process occurring during manufacture.

8. Tears, Breaks and Cuts. Such evidence holds vast potential for individualization. One compares questioned pieces or fragments with known pieces or fragments that can be associated with a particular person or place. One is looking for a “jigsaw fit” or “physical match”, which is a very compelling individualization. Often this is most easily accomplished with relatively large pieces, but can sometimes be effectuated with small remnants as well. For example, a paint chip precisely fits a scraped area on the fender of a car. Plastic, wood, cords, metal, paper and cloth can be treated similarly. Generally, breaks and tears provide the greatest potential for individualization because of the large number of surface irregularities which can be matched. However, sometimes cuts are also useful if there are surface features on the articles (such as background design, lines, handwriting or typing, grain structure, etc.) which can be matched.

9. Mutual Transfer of Matter. This is what occurs when two surfaces becames mutually affected by a contact during an assalt that there is a two-way transfer of material which can later link both objects. For example, when two cars collide they both commonly leave paint marks on each other. Dust, glass particles, hairs, fibers, vegetation and pollen can all be similarly transferred. In some cases, the transfers appear to be one-way because the amount of material transferred the other way is simply too small to be of significance. Individualization is the objective.

10. Deposits, Dispersals and Residues. Basically the same classification as above except that no actual contact is required. Fallen hairs, dust fall, spattered blood, and gunshot and explosive residues are examples. As above, individualization is conceivable.

11. Nature of the Evidential Material. Here identification alone is the principal or only objective. Often illegal drugs fall into this category, as do most alcohol tests.

12. Classification by the Appropriate Laboratory Approach Evidence is categorized depending on whether it is to be identified, individualized or used as an aid in reconstruction.

• Identification, alone, is required most commonly in the context of controlled substances; the very presence of a particular substance (and possibly in a particular amount) proves an element of the crime. In the same way, an element of the crime rape is proof of penetration by finding semen in the vagina, for example.

• Very often it is desirable to try to individualize a piece of evidence. To continue with rape, the presence of semen in the vagina establishes an important element of the crime. But DNA or other serological testing has the potential to prove or imply that the semen came from a particular suspect. Similarly, toolmarks, bullet marks, fingerprints, palmprints, shoeprints, broken glass and other torn, broken or cut surfaces offer the potential for compelling individualizations.

• Finally, reconstruction may be attempted when there are blood spatters or stains, large fragments of broken glass, or bullet holes through two or more materials which might yield clues as to trajectory, position of shooter, and so on.

This scheme is also a very useful way of thinking about evidence.

In short, there is not one single way to think about physical evidence. All the foregoing schemes have times when they are useful, and frequently a combination of schemes is informative. However, overall it is the last three methods which are the most generally valuable. No matter which way(s) may be best for categorizing any particular evidence, the job of the analyst will then be one or more of the following: identification, individualization, reconstruction. Alternatively, one may say that the criminalist’s job includes analysis and interpretation. The two sets of terms are intimately linked, as will be explained later. Which of these may be useful depends on the item and the case. We now examine each in somewhat more detail than previously. Identification Often this is the first step in analyzing the evidence. One must know precisely what it is one is dealing with, and this is the question identification seeks to answer. Identification may be both qualitative (e.g.: a powder contains both cocaine and sucrose) and quantitative (e.g.: 11% cocaine and 89% sucrose). Sometimes identification is all that is required; this is especially true in cases of controlled-substance possession. Other times identification is simply the first step in a process ultimately geared toward establishing an individualization. For instance, a dried sample of a red material is scraped at a scene. Is it blood? And if so, is it human blood? Supposing that the answers to these questions are both ‘yes’ then the identification would be complete. But it is likely that one would then perform DNA or other serological tests to try to individualize the blood to a particular victim or suspect.

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The nature of identification is to assign to a particular type of substance or object a set of class characteristics. These characteristics are associated with a group, and all members of the group have the same name and possess identically the same class characteristics. Thus, class characteristics are not individualizing. Establishing class characteristics of chemical materials requires considerable preliminary work on standard substances to ensure that a series of tests is available to reliably and unequivocally identify a particular substance and at the same time exclude every other possible substance. For instance, the test for cocaine must be developed using pure cocaine standards, and the test must not be positive for any substance other than cocaine. Testing may be as simple as a single experiment, or may involve a number of sequential analyses. Once formulated, the appropriate analyses are recorded and shared. To prove that a questioned powder is cocaine requires that the substance behaves in exactly the same way as did the cocaine standards when subject to the previously developed tests. In so doing, we would say that the questioned powder possesses the class characteristics of cocaine and is therefore identified as cocaine.

One of the potential pitfalls of the identification process is that standard substances are of high purity whereas questioned substances have a history and purity that are often unknown to the analyst. Thus significant preliminary work may be necessary to separate the components of a mixture from one another (the cocaine from the sugar, for instance), followed by identification of each component. Another variable over which the analyst has no control is the quantity of sample available for testing. Standard substances are available in essentially unlimited quantities and so identification procedures usually presume the availability of a minimum amount of substance for testing. Especially after substantial preliminary separations there may be only a minute amount of each component of the questioned sample left for identification purposes. At this stage the experience and education of the analyst will have to guide him on how best to identify such small samplings. Any methodology adopted will have to be supported in a court of law. Individualization When perfectly accomplished, individualization is identification carried to the extreme where there is only one member of the class under consideration. In that case, we speak of class characteristics becoming individual characteristics. For example, the chances of any two people having one fingerprint in common is estimated to be 1 in 67 billion; it has been estimated that the odds (likelihood, probability) of any two persons possessing the same set of ten fingerprints is 1 in 1060. Such odds are so staggering as to defy comprehension, and fingerprint matches are considered to be definitive individualizations throughout the world.

DNA analysis is similarly impressive. Current technology often only examines a few loci (or positions), and even here it is not uncommon that the odds of two persons showing the same characteristics are 1 in 100 million. The more loci that are examined, the more discriminating become the odds. Perfect individualization is entirely conceivable by examining only about a dozen loci, and this is being done increasingly. Notice that both the fingerprint and the DNA discussions are phrased in terms of probabilities. At its heart, individualization is a matter of odds, and complete individualization requires the sort of overwhelming odds found in fingerprinting and DNA typing.

Also note that individualization is usually a matter of comparison of questioned samples with known samples (or exemplars) in order to determine whether or not they have a common origin. That is, a blood drop is recovered from a crime scene. The blood is subjected to DNA typing, and that record becomes the questioned sample. A suspect is then ordered to give a DNA sample, which is typed. This is the known sample. The two are compared. There are only four possible outcomes:

1. If the odds are overwhelming that they came from the same source, the complete individualization of the questioned sample is established and this may provide an important prosecutorial element at the adjudication stage.

2. If the odds are reasonable (but not overwhelming) that the two samples came from the same source, then we say that the known sample is consistent with the questioned sample. This is known as a partial individualization. Like a complete individualization, it can be compelling evidence at trial, particularly if it can be coupled with other pieces of evidence.

3. If the two do not compare, the possibility of common origin is excluded, which may or may not remove suspicion from the suspect. Nevertheless, exclusion is a perfect proof of non-association between the suspect and the questioned sample.

4. In some cases too little sample is present for the requisite testing and so no individualizing information can be obtained.

Besides fingerprints and DNA, other evidence where there is a high potential for individualization includes bullets and cartridge casings (providing the weapon is recovered), striations in plastic bags, handwriting, tracks, imprints,

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indentations, and physical matches (or jigsaw fits) of a number of materials. However, the problem with these types of evidence is that there are no established odds concerning the likelihood of a match. For instance, if a questioned paint sample from a hit-and-run scene is a perfect jigsaw fit to a scratch on a suspect’s car, the evidence is compelling. But there is no way to know what are the odds of a random paint chip matching in this fashion. Certainly the probability is minuscule, but clearly not zero. This is one of the biggest problems in forensic science today. In a society increasingly dependant upon an ever increasing number of mass-produced goods, it is almost impossible to collect and categorize all unique specimens. Yet just this sort of data base is what is required if one is to meaningfully quote the probability associated with many comparisons. Except in rare cases (like fingerprints and DNA), a forensic scientist has to make a value judgement about the degree of individualization. Of course, such judgements can be challenged later.

In ascertaining the probability of a match between a known and a questioned sample, one must be very mindful of the fact that the probability of two uncorrelated events both occurring is the product of the probabilities that each event will occur separately. For instance, the probability of throwing a coin and having it land “heads” is ½. A second toss of the same coin is uncorrelated to the first, so the probability of observing a heads from a second toss is also ½. Thus the probability of throwing two heads in a row is the product, ½ × ½ = ¼. In the same way, in a series of N tosses, the probability of them all being heads is (½)N .

Probability is best expressed as a fraction. From the above, the probability of tossing five consecutive heads is (½)5 = 1/32 = 0.03125. We express the probability as the proportion fraction of events turning out a certain way : total outcomes

Thus the probability of tossing five consecutive heads is 0.03125 : 1 (or 1/32 : 1)

The “1" is understood to represent the totality of all possibilities. Of course, any proportion can be re-expressed by multiplying (or dividing) through the entire proportion by any convenient constant. Thus, fractional probabilities can be changed into percent probabilities by multiplying the above proportion through by 100 to yield 3.125 : 100

In this case we would say that of every 100 times one tossed five coins in succession, 3.125 of those sets of five tosses would yield five consecutive heads. Thus the probability of five consecutive heads is 3.125%. Finally, the “simplest whole number” expression of probability comes from dividing through the original proportion by the fraction on the left:

Here the interpretation is that once in every 32 tosses of five coins will one observe all five results being heads.

While all three of these ways of expressing probabilities are useful, one must remember that only when the probabilities are expressed as proper fractions (or decimals) is it fair to multiply them.

It is the “product principle” explained above that makes DNA typing so convincing. Recall that virtually every human cell contains 23 pairs of chromosomes; half of each pair is maternal, and the other half paternal. Each chromosome is a double helix of two strands. A strand is composed of a sequence of nucleosides, each of which consists of a sugar (deoxyribose) and an accompanying purine or pyrimidine base. In human DNA there are only four bases encountered: adenine (A), cytosine (C), guanine (G) and thymine (T). Within a single strand, adjacent nucleosides are held one to another via a phosphate linkage. On the other hand, the two strands comprising a single chromosome are held to each other via hydrogen bonding interactions between corresponding bases. The geometry of these interactions requires that an A in one strand match up with a T in the other, and that a C in one strand be opposite a G in the other. This correspondence is known as complementary base pairing. In a sense, then, one need only consider one of the two strands, since knowing the base sequence in this one strand makes the base sequence in the other entirely predictable. For instance, if one of the two strands is coded 3’-ATGTTC-5’ then the other strand will, at the analogous position, necessarily evidence the sequence 5’-TACAAG-3’.

The working portions of the chromosomes are the genes. In a gene, the base sequence essentially codes for protein construction from free amino acids. But between the genes are sequences of bases that repeat many times. In fact, probably more than 30% of the human genome consists of these tandem repeats. The tandem repeats seem to act as fillers or spacers between the coding portions of the chromosome.

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One of the most recent techniques in DNA analysis is short tandem repeat (STR) analysis. STR’s normally consist of repeating sequences of 3 to 7 bases, and the entire length of the repeat is usually less than 400 bases. As an example, one commonly used STR is located on chromosome 11, and is called TH01. TH01 consists of the repeating sequence AATG on one strand and TTAC on the other. From here on we will look only at the AATG strand, knowing that everything that is to be said will occur similarly for the corresponding TTAC portion of the second strand of the double helix.

The AATG sequence will be repeated anywhere from 5 to 11 times, and the length of the repeat is inherited. Thus, at the TH01 locus on the maternal chromosome 11, AATG may be repeated 6 times, whereas the paternal chromosome 11 may show the pattern repeated 8 times. This 6:8 combination is found in just 3.5% of the population. Thus, suppose a questioned blood drop is found at a crime scene. The sample is treated according to standard protocols for extracting the DNA and excising the TH01 locus. The amount of material is then greatly amplified by the Polymerase Chain Reaction (PCR), which allows ample material to be produced from as little as 1 ng of DNA. The STR TH01 is then analyzed for the number of AATG repeats found on both the maternal and paternal portions of chromosome 11.

Now, suppose that the victim’s known blood is treated in exactly the same fashion, and the maternal and paternal TH01 AATG repeats don’t match those found in the questioned blood. This is proof that the questioned blood cannot be associated with the victim. Also suppose that at some later time a suspect is identified. A warrant is issued requiring that the suspect submit a sample for analysis (blood or buccal swab). The suspect’s DNA is treated in the same way described above. Suppose now that there is a match in the maternal and paternal TH01 AATG repeats. This is a partial individualization. For U.S for example, Caucasians, the probability than any two random individuals will have an identical TH01 STR type is about 0.081 : 1; the probability is 0.109 : 1 for U.S. Blacks.

But the real power of the method is that several different loci are analyzed, not just the single TH01 locus. The FBI has selected 13 different STR loci, distributed among 12 chromosomes, for inclusion in CODIS (Combined DNA Index System). These are described in the following table:

STR Chromosome Probability of Identity (U.S. Black)

Probability of Identity (U.S. Caucasian)

D3S1358 3 0.094 0.075

VWA 12 0.063 0.062

FGA 4 0.033 0.036

TH01 11 0.109 0.081

TPOX 2 0.090 0.195

CSF1PO 5 0.081 0.112

D5S818 5 0.112 0.158

D13S317 13 0.136 0.085

D7S820 7 0.080 0.065

D8S1179 8 0.082 0.067

D21S11 21 0.034 0.039

D18S51 18 0.029 0.028

D16S539 16 0.070 0.089

The Probabilities of Identity measure the likelihood that two individuals selected at random will have an identical STR type. It is important to understand that these are independent probabilities and, as such, can be multiplied. Thus, if the questioned DNA and the suspect’s known DNA match in only the TH01 STR, the Probability of Identity is 0.081 : 1 (assuming that both are Caucasian), which can be re-expressed as the proportion 1 : 12. That is, the odds are 1 in 12 that

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the questioned and known DNA are unrelated. But if the two samples match in the first 5 STR’s listed above, the composite Probability of Identity becomes 0.075 × 0.062 × 0.036 × 0.081 × 0.195 = 0.0000026 : 1 (or 1 : 380,000)

Phrased another way, the odds are only about 1 in 380,000 that the two DNA samples are unrelated. But if the questioned blood and the suspect’s blood match in all 13 CODIS STR’s, the composite Probability of Identity is about 1.7×10–15 : 1 (or 1 : 5.9×1014), meaning that the odds that the two samples are unrelated is about 1 in 590 trillion. Since there are many fewer people in the entire world than this, the individualization is viewed as being complete. In the same way, if two fingerprints match in (let’s say) 12, the odds against them being from different sources is so remote as to be unbelievable, and the individualization is again judged complete.

It should be obvious that, given the overriding nature of probability in making for a compelling individualization, the process requires many uncorrelated matches and not just one or a few points of agreement. Thus, one would select a series of properties to observe for both a questioned and a known sample (i.e.: look at 7, or 9, or even all 13 of the CODIS STR’s). Hopefully the probabilities of a random match would be known for each of the comparisons. Then all the various properties are compared. If there is a match in every case, then the probability of such matching being random is the product of the individual matches. Ideally this is a staggeringly small probability that the samples are unrelated. Here it should be obvious that the best strategy is to focus on comparing properties which are inherently unlikely, so that the odds in each case are small, making the overall probability of non-association extraordinarily minute. In the end, the criminalist will have to render an opinion about whether or not the sample originated from the same source. If any one comparison of properties failed, then his answer will be an unequivocal ‘no’. If all of the comparisons were favorable and if the overall probability is staggeringly small that the samples are unrelated (as with fingerprint or DNA matches), then his answer will be an unequivocal ‘yes’. As mentioned before, the problem often is that the exact probabilities are unknown, so the analyst must base his guess of the probability on education and experience, and such subjective data is open for rebuttal or counter opinion. Partial Individualization As was noted in the foregoing discussion, there is a broad middle-ground between simple identification and complete individualization; that area is called partial individualization. It is quite likely that any piece of physical evidence (excepting for things like DNA, fingerprints, physical matches, tears, cuts, etc.) can only be partly, not completely, individualized. Here, again, it is probability that is the controlling factor.

A good example of this concerns a drop of blood which was found next to a bloody shoeprint at the home of Nicole Brown Simpson (read this trial on internet). Eventually the drop was subjected to DNA typing, but at first it was simply examined using more classical serological tests.

Each way one sort of blood differs from other blood samples is called a factor. Many of the different factors are due to the presence or absence of various antigens on the surface of the red cells, but there are other varieties of factors as well. First the drop from the Simpson home was typed for its ABO factors, and found to be of type A. However, about 33.7% of the population is type A, so this is not a very compelling individualization. The same droplet was then typed for other factors, and was found to contain the EsD 1 factor (which occurs in 79.6% of the population) and the PGM 2+,2– factor (which occurs in about 1.6% of the population). (NOTE: the percentages quoted are those which were given at the subsequent trial, and are different than the corresponding values quoted in the text). No one of these factors is very individualizing, but the odds of all three being simultaneously present (assuming that the factors are uncorrelated) is 0.337 × 0.796 × 0.016 = 0.0043 : 1 (or 1 : 230). Thus only about1 in every 230 people would be expected to possess all three factors simultaneously. O. J. Simpson’s blood placed him among the 0.43% of the population which possesses all three factors, while the blood of Nicole Brown Simpson and Ron Goldman did not match one or more factors, thereby excluding each of them as the source.

Certainly a 1 in 230 probability is not the sort of staggering odds required for a complete individualization. Yet the odds are well beyond what is required for identification of the sample as being human blood. This is the nature of partial individualization: it is essentially a technique of finding ways of placing a sample into smaller and more refined classes; yet the classes are still large enough that class characteristics have not shrunk to individual characteristics. While O. J. Simpson’s blood is consistent with the drop found at the scene, so would be the blood of about (0.0043)×(280,000,000) = 1,200,000 other people.

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Laypeople are often disappointed to find that most physical evidence can only be partly rather than completely individualized. However, there is great value in partly individualized physical evidence. First of all, there is the cumulative effect of such pieces. In the Simpson case above, for example, the single drop of blood referred to above was not the only evidence. Hairs, fibers, clothing and witnesses also tied O. J. Simpson to the scene or crime. For trial a case is fashioned around many diverse elements, all of which are meant to point towards the guilt of the accused. Each component may not definitively link the defendant to the crime, but the preponderance of many different types of evidence can be a difficult burden to overcome. Further, physical evidence has the appearance of being objective. Because scientists are held in high esteem by most members of our society, and because juries are generally composed of laypersons rather than specialists, it is likely that scientific evidence is given a substantial weight in the deliberation processes of most juries. As such it is more difficult to refute than other, more subjective types of evidence such as eyewitness, informant testimony and confessions, all of which can perhaps be successfully challenged during cross-examination.

In general, itt is a difficult matter to say precisely when one crosses the line between partial individualization (or class characteristics) and complete individualization (or individual characteristics). Certainly the 1 in 230 odds of finding a person with the same three blood factors as were present on the drop of blood in Nicole Brown Simpson’s home is a partial individualization. And just as surely, the 1 in 590 trillion odds that two unrelated DNA samples match in all 13 of the CODIS STR loci, or the 1 in 67 billion odds that two unrelated fingerprints match in 12, represent true individualizations. But the odds mentioned above are easy to interpret simply because they are available. Remember, most times the calculation of such odds is impossible.

How many similarities have to exist in two bullets to be sure they were fired from the same gun? How many layers of paint must be present in a chip to individualize it to a single car? How many points of similarity must there be to definitively say questioned and known handwriting samples are attributable to the same person? The answers to these and many other similar questions are unknown. It is the existence of these uncertainties that causes honest disagreements between forensics experts at trial. We hope and assume that the actual analyses are unbiased and objective, but the interpretation of the results is another matter entirely. One expert may consider a set of striations left by a tool to be individualizing, while another might consider such evidence to be only partly individualizing. No rigorous data exist to support or refute either argument and, in the end, the jury will have to decide how much weight to give to the various opinions and pieces of evidence. In this regard, it is wise to have made as many comparisons as possible, remembering that the more comparisons in common the much greater likelihood of a strong association between questioned and known samples. Thus hairs, for instance, are compared not just for color but also for diameter, scale pattern, pigment granule structure, and other characteristics. In the same way, multiple analyses increase the chances of exonerating an innocent party by virtue of increasing the likelihood of unearthing a mismatch.

Reconstruction Identifications and individualizations are the activity of the criminalist. In contrast, reconstruction is a team effort; it must involve police investigators, medical examiners and criminalists. The goal is to take the physical evidence from the scene and/or victim in conjunction with testimony and statements from victims, witnesses and others involved and then come up with a likely scenario of how the crime progressed.

The physical evidence can answer such questions as: Was the body or any other object(s) moved? If so from (or to) where, and for what reasons? Were there actions taken to cover-up the crime or to mislead police? How many people were present at the scene? Where was the shooter positioned relative to the victim? How did the perpetrator enter and leave the scene?

For reconstruction to be successful the scene must have been processed very well. For example, one way to tell if a body has been moved is to examine whether or not livor mortis is present in those un-constricted spots nearest the ground. One can also tell if the victim was clothed or disrobed after death because livor mortis will not form in areas of the body constricted by clothing. Clearly if police or medical personnel have already moved the body it becomes difficult or impossible to make such judgements. Likewise it is crucial to know how many people were at the scene but if law enforcement personnel are allowed to contaminate the scene it will be difficult or impossible to determine the answer to this question.

Just as damaging as allowing the scene to be disturbed is to not document it fully. Notes, photos, videos and sketches are indispensable if reconstruction is to be successful later. As already noted, the lead investigator will often be thinking of reconstruction as early as his preliminary walk-through of the scene. He will imagine one or several scenarios whereby

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the crime might have occurred, and will then plan his search of the scene so as to collect evidence which will tend to prove, disprove or discriminate amongst these various scenarios.

Skills that criminalists can bring to a reconstruction include determining the probable trajectory of bullets, analyzing blood spatter patterns to determine how the perpetrator and victim moved relative to one another during a struggle, what wounds were inflicted at each stage of the crime, analyzing a victim’s clothing to estimate how far away was a shooter, swabbing the hands of suspects and victims to test for powder residue (which would prove they used a firearm), and so forth.

When all this evidence is put together it can potentially give an account of what happened, all the way from right before to right after the crime. This may be quite useful in several respects. In the investigative stages the reconstruction can be used to suggest that an investigation is proceeding along the right (or wrong) path. Also, there are often no witnesses to crimes so reconstructions can provide both investigative leads and one or a few likely scenarios for what may have happened. Even a victim who survives is often of little use in providing recollections of the crime due to the trauma and anguish experienced. Eyewitnesses, too, are usually unreliable. They have difficulty recalling what occurred, particularly if there was a complex sequence of events. Also, they may change their testimony over time. Such alterations can be for self-serving reasons, or out of fear, or simply because their memories falter. Suspects have a vested interest in lying if they are guilty, and may be too shaken-up to give an accurate statement if they are innocent. Thus the reconstruction can help sort out the truth among what may be numerous conflicting stories. Finally, one of the most compelling uses of a reconstruction is to “tie all the pieces together” for a jury, helping them understand how the motivations and actions of various parties are explained by the physical evidence that has been presented at trial.

Analysis versus Interpretation At the beginning focused on three activities commonly associated with criminalists: Analysis Interpretation Reporting the results and expert testimony However, we have actually been talking much more about the goals of forensic science as regards examining physical evidence, namely Identification Individualization Reconstruction What is the connection between these two lists? Analysis is the objective part of forensic science. Analysis consists of making one or a series of chemical or physical measurements; these may be either direct (length, mass, volume, etc.) or indirect (determining the mass spectrum or IR spectrum of a sample). But in any case the results should follow accepted protocols or, when appropriate, should represent new protocols developed by experts to handle a novel type of evidence or a special situation. There should be little disagreement between experts concerning the results of analyses. For example, in a drug-possession case the suspect was apprehended in possession of a plastic bag containing 2 g of a white powder. The powder was separated using standard methods into two components which were analyzed separately. Component 1 was heroin, and component 2 was lactose; the heroin accounted for 3% of the sample and the lactose the remaining 97%. Thus the suspect was in possession of (0.03)×(2 g) = 0.06 g of heroin. This is an analysis. Assuming that standard protocols were followed for the separation and subsequent identifying tests, and that adequate documentation of the testing and results was prepared, and that the chain of custody can be suitably proven, then there is little to argue about.

Usually all of identification is concerned with analysis, and so are the comparisons that are used in partial or complete individualizations.

In contrast, interpretation can be quite subjective. It consists of forming a hypothesis or theory, taking all the objective evidence and working backward to tie the observations together into a pattern or form which is consistent with all the data and which provides useful information about the crime. Reconstructions are usually interpretations. The reconstruction must fit all the analytical data, yet it is not proof. Remember that this is one of the great pitfalls of the inductive method: good data can support false hypotheses.

Less obvious perhaps is that many individualizations involve some interpretation. The drop of blood found at Nicole Brown Simpson’s house is a good example. Serological tests (which are analyses) showed that only about 1 in every 230 people would have the same blood factors as were present in this drop. O. J. Simpson’s blood possessed all three factors,

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while the blood of the two victims did not. Clearly the prosecution and their forensic experts interpreted this as evidence of O. J. Simpson’s culpability (guilt). They also combined this result with many others, all of which pointed to (but did not necessarily prove) the guilt of the defendant. Just as clearly, the defense and their experts reminded the jury that 1 in 230 odds meant that there were 1.2 million suspects in addition to O. J. Simpson. The nature of interpretations is that they are much more likely than analyses to engender disagreements and dissenting opinions. In the same way, if fingerprints show 12 points of comparison, it is considered a complete individualization by many forensics experts in the US. The standards in other countries sometimes require either fewer or more than 12 points of comparison. Thus there is some disagreement about the precise point at which a fingerprint has been completely individualized. By adopting any particular cut-off value one is engaging in interpretation.

The distinction between analysis and interpretation can be subtle. Suppose a fingerprint is found at a scene and is determined to match a fingerprint of a suspect. Providing the experts can agree that the particular number of points of comparison found (12, say) constitutes a complete individualization, then this is an analysis. But even then all it proves is that the suspect was present at the scene at some time. Nothing more. The inference that he was present during the commission of the crime is an interpretation, and certainly an interpretation which is likely to figure prominently in a later reconstruction. Yet because this is speculation and not analytical fact, it can be refuted by explaining how and why the suspect may have been present at the same location some other time. Reporting the Results and Expert Testimony This is perhaps the most formidable task a forensic scientist must undertake as the court is a scary place. In the early stages, highly technical data and interpretations must be conveyed to law enforcement personnel and prosecutors. Later, judges and juries must be made to comprehend the same complicated issues.. As a criminalist, you should view the court as a “teaching opportunity”. You mission is not to convince the jury but to teach them about what you found and why you feel it represents the best explanation of what you feel happened. Be prepared and be confident that your training, experience, examination and conclusions are sound and represent the unbiased truth to the best of your ability. You should view the court as a “teaching opportunity”. You mission is not to convince the jury but to teach them about what you found and why you feel it represents the best explanation of what you feel happened. Trial preparation As a forensic witness you should anticipate how you would show a jury what you found and how it pertains to the case using all documents and illustrations available to you. Record negative or normal observations in your raw data to so as to document why you eliminated other possible explanations. Anticipate the opposite side’s explanation and be prepared to counter or support it by the demonstration of the right facts. As a part of pre-trial preparation, prosecutors and defense attorneys will spend considerable time with their own forensic witnesses prior to trial to make sure that the attorneys, themselves, understand the technical aspects of the expert testimony and that they are equipped to ask the proper questions. The attorneys will also satisfy themselves that each expert witness is capable of explaining results in a manner comprehensible to the typical jury. Forensic experts should resist the pressure to make unbending or unqualified statements in their testimony as well as be forced to testify as an expert in area they are not trained nor have creditable experience. In case they required to testify in court for issues they personally did not examine or analyze, they should avoid being very none committal about anything they might be asked to testify about. Hence they are required to establish what to say and cannot testify based on their training and experience and as well as their direct involvement in the examination and/or analysis of the evidence.

Through preparation of charts and graphics and through sufficient rehearsal it is hoped that the jury will be capable of understanding and believing the results. However, sometimes juries, and even attorneys, find it difficult to cope with mounds of these technical evidence . And in the end it hardly matters if the attorneys are having difficulty, but when the jury gets lost the case is in jeopardy.