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Assignments / quizzes 30% Midterm exam30%

Final exam- 40%

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By the end of this learning unit, students willbe able to answer some basic questionsabout Forensic Chemistry: What is Forensic Science?

How is chemistry used in Forensic Science?

What determines the value of each item ofevidence?

Is the analysis for each item of evidence the same?

What type of information allows for an exclusivelink?

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Forensic Science: applies science principles,techniques, and methods to the investigationof crime.

Role of forensic scientist Analyse physical evidence in a crime laboratory and

spend little time at the crime scene. Do not involve directly in solving the crimes.

Crime Scene Investigators/police - Collectevidence to solve the crime

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Involvement ofvarious individualsin an investigation

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A large number of forensic scientists arechemists.

Forensic chemists employ their knowledge of

chemistry to analyze evidence such as fibers,paint, explosives, charred debris, drugs, glass,soil, documents, tool marks, and firearms.

Forensic chemists also use their knowledge fortoxicology (the study of poisons and theireffects), fingerprints, footwear impressions, tireimpressions, and hair analyses.

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Although many forensic analyses require theexpertise of a chemist, chemistry is not theonly discipline that contributes to theextremely vast and truly interdisciplinary field

of forensic science.

Other disciplines and professionscontributing to the field include engineering,

computer science, entomology, anthropology,pathology, physics, nursing, and psychology,among many others.

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Historically, forensic scientists are generalistswho would analyze all types of physical evidence.

Forensic generalists are slowly being replaced byforensic specialists due to the ever-increasing

complexity of the field of forensic science.

Forensic chemistry, for example, is now aspecialized field of forensic science.

The forensic chemist does not typically analyzebiological evidence or carry out DNA analyses.

These analyses are typically performed by aforensic biologist.

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With the wide variety of evidence that may beanalyzed by the forensic chemist,subspecialization is also quite common.

It is not unusual for a forensic chemist to begiven a subtitle such as firearms analyst,trace evidence analyst, fingerprint analyst, or

drug chemist.

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Forensic chemists may also be given the titleof criminalist.

The branch of forensic science heavily

enriched in chemistry and biology applicationsfor the analysis of physical evidence.

Criminalistics encompasses a broader area of

forensic science than just forensic chemistryand includes most of the areas of forensicscience practiced in a traditional crimelaboratory.

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Introduction to Forensic Science: BasicCrime Lab

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Physical science unit: applies principles andtechniques of chemistry, physics & geology toevidence evaluation; examinations of soil,drugs, glass, paint, explosives etc are

examined Biology unit: applies principles and

techniques to identify DNA for profiling,stains & body fluids, hair & fiber comparison,

wood and plants

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Firearms unit: examination of firearms,discharged bullets, cartridge cases, shot gunshells, ammunitions, garments and otherobjects examined to detect discharge of

residues etc.

Document examination unit: handwriting andtypewriting on questioned documentsstudied; analysis of paper & ink; erasures,obliterations, document charred or burned

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Photography: examine and record evidence;digital imaging, infrared, ultraviolet, and X-ray photography techniques make invisibleinformation visible; court room presentations

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Toxicology unit: body fluids & organsexamined determine presence or absence ofdrugs & poisons often this is shared with themedical examiners or coroners office

Latent fingerprint unit: examination of latentfingerprints submitted with other labexaminations

Voiceprint analysis unit: cases involvingtelephone threats, tape-recorded messages

may use to identify persons Sound patterns are suppose to be unique to the

person & and are captured on a voiceprint

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Physical properties are properties of asubstance that can be described or displayedwithout requiring a chemical change.

For example, sulfur is yellow, cocaine is awhite solid, and the density of a glassfragment broken from a windowpane at a

crime scene is approximately 2.5 g/mL.

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Chemical properties are properties of asubstance that can be described through achemical change only.

For example, a chemical property of bakingsoda (sodium bicarbonate) is its reactivitywith vinegar (acetic acid) to produce carbon

dioxide bubbles

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Although the exact manner in which thephysical and chemical properties are analyzedfor each substance differs, the analyses areall based on the principles of the scientificmethod.

The scientific method: The process ofinvestigation involving observation andhypothesis testing.

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The scientific method begins with observations.

Scientists attempt to organize observations andlook for trends or patterns.

When the scientists find what appears to be arelationship among the observations, they suggesta hypothesis (an educated guess) that tentatively

explains what is being observed.

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Forensic Chemistry: The scientificmethod

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An unknown substance is submitted to a crimelaboratory, The forensic chemist will first observe theproperties of the substance. She may notice that thesubstance is a crushed and dried green-leafymaterial.

Next, she will suggest a hypothesis as to the identityof the substance: The unknown substance ismarijuana.

This is an extremely crucial step because the analysisto be performed (the plan for testing the hypothesis)is different for each unknown substance.

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The chemist will then devise a plan to test the hypothesis:

to view the substance under the microscope looking forproperties of crushed marijuana leaves.

If the microscopic observations validate the hypothesis,she will develop a subsequent plan to further validate thehypothesis: to react the marijuana leaves with Duquenois-Levine reagent to observe chemical properties.

If the microscopic features do not validate the hypothesis,she will suggest and test an alternative hypothesis: Theunknown substance is oregano.

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In chemistry, physical and chemicalproperties are used to characterize anddistinguish one compound or element fromanother.

In forensic chemistry, these properties aid inthe identification classification andindividualization of physical evidence.

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A plan is devised to test the hypothesis.

The plan is carried out and further observationsare made.

If the new observations contradict the originalhypothesis, a new hypothesis is suggested andtested.

However, if the new observations validate theoriginal hypothesis, the scientists often chooseto devise a subsequent plan to further validatethe hypothesis.

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After a police officer or investigator hascollected evidence at a crime scene, someevidence may be brought to the crime lab fora forensic chemist to analyze.

The chemist follows a specific process, basedon the scientific method, for analyzing

evidence.

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Samples collected from a crime scene andbrought to the lab for analysis are calledquestioned samples because the identities andorigins of those samples are unknown.

In order to draw conclusions about the identity ororigins of questioned samples, the forensicchemist will need known samples as a reference.

A known sample might be collected as part of theevidencefor instance a hair sample collectedfrom a suspect.

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Forensic analyses may be performed to identify a questioned sample or

compare a questioned sample to a known samplefor the purpose of determining the source or origin

of the sample (where it came from).

The results of such comparisons can link aquestioned sample and several known

samples either to a class of samples withseveral possible origins (classification) or to asingle origin (individualization).

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When a questioned sample is submitted to acrime laboratory for analysis, the first task isidentification.

For example, if a white powder is submittedfor analysis, the primary objective will be todetermine its identity. If the powder issuspected of being a controlled substance,the forensic scientist will carry out a series ofanalyses to identify the powder

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Two types of analysis can be used to identifythe substance: presumptiveand confirmatory.

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However, a number of similar compounds (all

containing a nitrogen atom with one hydrogenatom and two attached carbon atoms) will alsoproduce a deep blue-colored product.

This analysis does not confirm that the substance

is methamphetamine, but it does reduce thenumber of possibilities.

Presumtive analyses are usually quick andinexpensive to perform.

When presumptive analyses are negative, theyexclude potential drug candidates; when they arepositive, they direct the forensic scientist towardviable confirmatory analyses.

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Confirmatory analyses identify a questionedsample absolutely. These analyses use the unique chemical or

physical properties of a substance for thepurpose of identification.

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Typically, confirmatory analyses require moretime and expense than presumptive analyses.

These analyses often require the use ofsophisticated chemical instrumentation tomeasure the unique properties that lead toidentification.

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Thin layer chromatography (TLC) Analysis of inks & drugs

Chromotography- sample cleanup &analyte isolation

Confirmation of tentative identification Infrared spectroscopy

Gas chromatography-mass spectrometry (GC-MS)

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Many forensic analyses end with identification(for example, identifying an unknown substanceas a drug, explosive, or accelerant used in arson),but some proceed on to comparison.

Comparative analyses are to link a questionedsample and a known sample to a common origin.

The origin may be broad, resulting in aclassification, or exclusive, resulting inindividualization.38

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Class characteristics are properties of asubstance that are shared by a group ofsubstances, but are not unique to allsubstances of a single origin.

They allow for the placing of a questionedsample into a class or group of severalpossible origins.

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For example, a class characteristic of hair isits color.

If a questioned hair sample is brown, it couldbe determined that the hair originated from aperson with brown hair.

These properties are analogous to those usedwhen conducting a presumptive test for thepurpose of identification.

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Not only are class characteristics common toother substances, but they may also varywithin a substance.

A class characteristic that varies within asubstance is called natural variation.

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Virtually all physical evidence has classcharacteristics.

These characteristics are more common than

individual characteristics.

Many items of evidence, like hair, fiber, glass,soil, and paint, routinely only have classcharacteristics.

In other words, classifications are more commonthan individualizations.

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The ability to exclude is a very powerful aspect ofclass characteristics.

A comparative analysis excludes a questioned

hair from originating from the suspects head,this information is just as important asindividualizationthe suspect may beexonerated (set free of guilt).

Individual characteristics are properties of asubstance that are unique and can be used toestablish origin.

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For example, if the brown hair samplecontained enough DNA in its root for a DNAanalysis, the DNA would be considered anindividual characteristic that would

exclusively link the hair sample to a singleorigin (person).

Many items do not have individualcharacteristics, so investigators must rely onclass characteristics.

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Scientific evidence can be described as: Inclusive Exclusive

Ex. of inclusiveevidence:

Red fiber from a crime scene belonged to the sameclass as fibers from a suspects red nylon jacket The jacket is included in the population of items

that could been the source of the fiber in question.

Ex. of exclusiveevidence: Fibers from the jacket have a different cross section

that of the fiber found at the scene The jacket could not have been the source

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Direct evidenceis known to a person bypersonal knowledge Eyewitness testimony

Such evidence, if found to be true, would prove apoint in contention without requiring any additionalanalysis or inference

Circumstantial evidence Evidence that requires inference to move logically

from the information provided to the answer to aquestion

Ex: if blood is found on a knife, but not directly on

the suspect DNA typing showed that the blood matched that of a

suspect to 1 person in 6 trillion

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The chain a paper form that tract evidence

from its creation or collection to its finaldisposal.

A Cradle-to-grave document that completelydescribes the history of a sample or an exhibit

constituting evidence. A chain is initiated when the sample is collected

or created and is updated each time the sampleis transferred from one person to another.

Maintenance of the chain is a fundamentalresponsibility of any forensic analyst.

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Analytical chemistry in the forensic field: Forensic toxicology

Work with biological evidence

Follow the trail of drugs and poisons ingested by

human or other organism Often associated with death investigation

Forensic chemistry

Work with physical evidence

Often employ in crime labs

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Deal with: Drugs

Trace

Fingerprints

Firearms

Arson

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Apply scientific disciplines to physical evidence

A Forensic chemist is a professional chemist who analyzes evidence that is

brought in from crime scenes

reaches a conclusion based on tests run on that pieceof evidence

to identify and characterize the evidence as part of thelarger process of solving a crime.

rarely conduct any investigative work; they handle theevidence collected from the crime scene

Evidence may include hair samples, paint chips, glassfragments, or blood stains.

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Often need to give expert testimony in court must be able to give an impartial explanation

to the jury that will assist in a final judgment

forensic chemists analyze the evidence

but do not determine the verdict.

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Forensic chemist should be: Assuming nothing

Be resourceful

Think outside the box

Be creative

Know their limitation

Be flexible

Be persistent

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May conclude that an evidence object & areference object show similar traits

Must understand and communicate thelimitations inherent in the conclusion

limitations are a combined function of the nature of the traits the sensitivity and resolution of the

detection methods the state of the evidence