Types of Evidence

“You can observe a lot by just watching.”

-Yogi Berra

• What is evidence? (review notes!!)– Something that tends to disprove or establish a

fact. – Includes • Documents• Testimony • Objects

Two types of Evidence• Testimonial Evidence– Statement made under

oath– What is said in court by a

competent witness– Also called direct

evidence or prima facie

• Physical Evidence– Tangible items that tend

to prove some material fact

– Aka real evidence

Testimonial evidence• Eye witness accounts provide important evidence• Eye witnesses Heavily influence juries• Fear and stress involved in witnessing a crime can either sharpen the senses or confuse

them• But are they accurate?

– New information affects eye witness accounts• Mug shots• Leading/Suggestive questions

– Can change memory of witness, even those trying to be fair or honest

– Memory errors• Time between the crime and questioning of witness can affect what they remember

– Perception errors• Too dark• Encounter too brief• Presence of weapon diverted witnesses attention

Points to consider in Reliability of Eye Witness Accounts

• Type of crime and how witness saw it– Research shows witnesses are better at remembering certain characteristics (hair color and sex) than others (age,

height ,and specific race)– If witness is physically similar to offender, they will give a more accurate account

• Victims of serious crimes sometimes have more accurate memory over long periods of time– Relive event– Presence of weapon=sharpen sense/awareness

• Some types of witnesses are better at remembering than others– Children– Older adults– Learning disabilities and mental disorders– Alcohol and drugs– Head injury

• Interviewing Techniques or How information is retrieved can make a difference in accuracy of witness’s account– Witnesses are better at answering questions about what happened than answering questions regarding description of

offender• Open-ended questions get better answers

– Careful choice of words influence memory– Ex. Ask witness to describe what defendant was wearing rather than what color was his shirt– What would be a bad question?

Other important factors when weighing an eye witnesses account

• Relationship of witness with the accused• How much time passed between offense and

identification• Whether the witness already identified the (or failed

to identify) the defendant• Whether the witness has already identified someone

else****most known cases of an innocent person being

convicted happened because of a mistaken eye witness

"Wherever he steps, whatever he touches, whatever he leaves even unconsciously, will serve as silent witness against him. Not only his fingerprints or his footprints, but his hair, the fibers from his clothes, the glass he breaks, the tool marks he leaves, the paint he scratches, the blood or semen he deposits or collects -- all of these and more bear mute witness against him."

—Dr. Edmond Locard

Locard’s Exchange Principle

"Every Contact Leaves a Trace"The value of trace (or contact) forensic evidence was first recognized by Edmund Locard in 1910. He was the director of the very first crime laboratory in existence, located in Lyon, France.

The Locard’s Exchange Principle states that "with contact between two items, there will be an exchange." For example, burglars will leave traces of their presence behind and will also take traces with them. They may leave hairs from their body or fibers from their clothing behind and they may take carpet fibers away with them.

Physical Evidence• Tangible items that tend to prove or disprove a fact• “Real Evidence”• Physical evidence refers to any material items that would be present at the

crime scene, on the victims, or found in a suspect’s possession. • Type of evidence forensic scientists are most interested in• Forensic scientists will…

– Observe physical evidence– Determine identity– Determine origin

Physical evidence…

• Can be any material or object• Take any form– Large as a building– Fleeting as an odor– Small as a hair– Microscopic as DNA

• Much more reliable than testimonial evidence

Common Types of Physical Evidence

Drug and toxic substance Resins, plastics Fingerprints

Paints Explosive residues Hair

Gun shot residues (GSR) Serial numbers Tissues

Firearms and ammunition Documents Pollen

Impressions Fibers Wood material

Petroleum products Soil Feathers

Alcohols (esp. ethanol) Glass Bones

Rubber material Blood and other body fluids

Tool marks

Properties of Physical Evidence

• Physical– Can be observed and measured– Physical changes do NOT change the identity of a

substance– Properties that do not change the chemical nature of

matter– Intrinsic/intensive physical properties

• Does NOT depend on the amount of a substance• Examples

– Density– Melting point– boiling point– Freezing point– Viscosity– Refractive index– Malleability– Luster– color

– Extrinsic/extensive physical properties• Depends on amount of substance• Length, volume, mass, weight etc

• Chemical– Properties that do change the chemical nature

of matter– Can be observed when object or substance

changes its chemical composition– Observed when one substance reacts with

another• ONLY observed during a chemical reaction

– Signs of a chemical change• Formation of gas (bubbles)• pH change• Change of color (indicator)• Formation of precipitate• Change of smell

– Examples• Digestion• Respiration• Photosynthesis• Combustion• decomposition

• Determining origin of a substance almost always involves a comparison of object or substance itself with something similar or with something similar that the scientist knows the origin of

• Compare with a known or “control”

The Innocence Project

• National organization dedicated to exonerating wrongfully convicted people through DNA evidence

• Eye witness misidentification is the number one cause of wrongfully convictions nationwide

• As of 2008, the Innocence Project exonerated 212wrongfully convicted poeple

Types of Physical Evidence

• Trace Evidence• Transient evidence• Conditional Evidence

• Evidence can also be classified as:– Indirect Evidence (Circumstantial Evidence) vs. Direct

• Individual evidence vs. Class evidence

Trace Evidence• Trace evidence refers to physical evidence that is found in small but measurable

amounts, such as strands of hair, fibers, or skin cells.

Not all evidence is permanent…• Transient evidence

– Temporary evidence– Can be easily changed or lost– Usually observed by first officer on scene and must be recorded at that

time• Examples?

– Odors• Perfume, cigarette smoke, gas

– Temperature• Coffee pot, car hood, water in bath tub, dead body

– Imprints• Footprints in sand, fingerprints in dust, teeth marks in perishable

food

Conditional Evidence• Produced by a specific action or event at the scene • Must be observed and recorded• Examples– Lights– Garage door– Doors– Windows– Position of body– Position of furniture

Indirect Evidence

• Evidence that does not prove or disprove a fact in question

• Evidence providing only a basis for inference about a disputed fact

• May prove something like the possession of controlled substances or driving under the influence

Circumstantial Evidence

• Evidence based on suggestion rather than personal knowledge

• Circumstantial evidence indirectly proves a fact. – It is evidence that requires or allows a trier of fact to make a deduction

to conclude that a fact exists.

• The more circumstantial evidence there is, the greater it weighs

• Probability and statistics important• Examples

– Blonde hair found in hand of murder victim with black hair– Size 10 sneaker print near the body– Both of these limit the pool of suspects

Circumstantial Evidence• A classic example of circumstantial evidence would be testimony from a witness who

arrived at a crime scene to find someone holding a smoking gun. The person holding the gun could have committed the crime in question, but he or she could also be an innocent bystander. A piece of corroborating evidence to support a case against the person holding the gun might come from another witness who testifies to hearing a gunshot seconds before the first witness arrived on the scene, suggesting that the murder would not have had a chance to get away.

• Essentially, circumstantial evidence paints a picture of the circumstances of the case. • Good lawyers are very talented at extracting circumstantial evidence in a way which

will support an end point AS WELL AS undermining circumstantial evidence by making the witness seem less credible, using a variety of techniques.

• The acceptance of circumstantial evidence in a case can make or break the verdict, especially when there is little direct evidence to link the accused with the crime.

• http://www.wisegeek.com/what-is-circumstantial-evidence.htm

Still don’t get circumstantial evidence?

• Circumstantial evidence is best explained by saying what it is not - it is not direct evidence from a witness who saw or heard something. Circumstantial evidence is a fact that can be used to infer another fact.

• Indirect evidence that implies something occurred but doesn't directly prove it; proof of one or more facts from which one can find another fact; proof of a chain of facts and circumstances indicating that the person is either guilty or not guilty.

• FOR EXAMPLE:– If a man accused of embezzling money from his company had made several big-ticket purchases in

cash around the time of the alleged embezzlement, that would be circumstantial evidence that he had stolen the money. The law makes no distinction between the weight given to either direct or circumstantial evidence.

– http://www.lectlaw.com/def/c342.htm

Value of Physical Evidence• Can prove crime has been committed

– Gasoline at a scene of a fire• Back up witness testimony or disprove it

– Test blood stains of suspects• Link suspect with victim or crime scene

– Broken glass of headlight in cuff of suspects pants at scene of hit and run

• Determine identity of people associated with crime– Fingerprints, DNA

• Allow investigators to reconstruct a crime– Blood spatter patterns

Significance of Physical EvidenceIndividual Evidence• Material that can be related to a

single source • Individualization always involves a

comparison• Narrows an identity to a single

person or thing• Examples

– DNA– Fingerprints– Handwriting– Some physical evidence

• Piece of glass that fits another piece like a jigsaw puzzle

Class Evidence• Material that can be associated with a

group of items that share properties or characteristics

• Object is similar to group of similar objects but not one single object

• Narrows an identity to group of persons or things

• Examples– Blue jeans

• We can use some individualization such as length, style, brand, shade, surface treatment but there are still thousands of jeans like that

Evidence

Direct Circumstantial

Physical Biological

Evidence Examples

Did you know? Most paint evidence submitted to a lab will come from hit-and-run cases involving automobiles.  

Paint

• Physical and chemical analysis of paint evidence (chips or residue) can indicate it’s class, such as automobile paint, house paint, nail polish, etc. The evidence can be compared to 40,000 different types of paint classified in a database, which can be used to identify a particular make or model of car or brand of tool.

• Paint evidence can also indicate individual characteristics if an investigator is able to find similarities between two samples, such as the color, number of layers, chemical composition, or a physical match between the edges of two paint chips – one from a tool and one from a crime scene.

Paint Layers Physical Match of Paint Chip Edges

Paint Transfer on a Car

Glass

• Glass particles can be found at various crime scenes, such as breaking and entering, hit and run, vandalism, or murder. 

• Glass at a crime scene is analyzed to determine its color, surface characteristics, tint, thickness, density, chemical composition, and refractive index (RI).

• The results of the tests provide clues about the crime and help investigators connect the evidence to a suspect or other object used in a crime, such as matching glass from a crime scene to a headlight to a suspect’s car.

The pattern of cracks in a windshield fracture can reveal information about speed, occupant position, and angle of impact. Magnified image of glass fragments

Explosives

• Explosive substances can be examined to determine its chemical composition to identify the type of explosive used and its origin.

• Traces of explosives found on a suspect’s clothing, skin, hair, or other objects may be matched to explosives from the crime scene.

• Materials used to make an explosive device will be compared to evidence found in the suspect’s possession to confirm a match.

Ballistics

• Characteristics of ammunition, firearms, and residue are examined to find matches between suspects and the evidence found at a crime scene.

• Chemical tests can reveal gunshot residue (GSR) on the hands, face, or clothing of a victim or suspect to indicate how close a person was to a fired gun.

• Rifling (grooves) in a gun barrel causes distinctive grooves, indentations and scratches upon fired bullets, which can be matched to the weapon that fired them.

• Police are able to search the National Integrated Ballistics Identification System (NIBIS) database to compare markings from bullets, cartridge cases, and shotgun shells to ballistic evidence.

Investigators can compare the striations on bullets to see if

they match.

Did you know? Caliber (handguns & rifles) or gauge (shotguns) refers to the size of the internal diameter of a gun’s barrel.

Fracture Matches

• When an object broken, torn, or cut, two unique edges are formed, which are referred to as fracture lines.

• These edges can be compared by the naked eye or with microscopes to see if they fit together , which indicates that they may have been part of the same object at one time.

• Investigators may compare the edges on pieces of tape, glass fragments, paint chips, pieces of a car from an accident, paper bag, etc. to find possible matches.

Impression Evidence

Shoeprints & Tire Tracks• Impression evidence can be photographed, lifted with tape, or cast with plaster to compare to a suspect’s shoes or tires. • Investigators will examine the evidence to identify the brand of shoe or tire based on its tread pattern and other physical features to provide leads in the case.• Shoes and tires will also show wear patterns after being used for a period of time as well as other features (scratches, nicks, and cuts) that can be used to match evidence to specific items. For example, shoeprints can be matched to a suspect based on how the treads on the shoes that are worn down due to that person’s walking style.

Bite Marks• Each of the 32 teeth in humans is unique due to age and wear.• Impressions and photographs of bite marks left on a victim, assailant, or other object at a crime scene can often be matched to dental records.

Tool Marks• Tiny nicks and chips form on the edges of a tool as it is used, which can be used to identify matches between evidence and suspects. • Tools may also pick up traces of blood or other substances that can be tested or have fingerprints that can be lifted.

Examples: Vomit and urine can be used to test for alcohol, drugs, and poisons. Cigarette butts may contain dried saliva. Semen containing sperm is valuable for DNA analysis. Blood can provide DNA evidence and blood spatter can provide clues about the crime.

Body Fluids

• Blood, semen, saliva, sweat, and urine can be analyzed to give investigators information about the crime as well as its victim or the suspect.

• Chemicals and ultra violet light can be used at a crime scene to find body fluid evidence. Areas with potential evidence are swabbed, bagged and collected in vials, which are air tight and have a low risk of cross contamination.

Images: http://biology.arizona.edu/sciconn/lessons2/Vuturo/vuturo/photos/desmus.gif

Fingerprints

• There are 3 types of fingerprint patterns: arches, loops, and whorls. Investigators also identify unique ridge characteristics in a fingerprint that can be used to identify a suspect or victim.

• AFIS (Automated Fingerprint Identification System) is a database used by investigators at local, state, and national levels to search for matches to fingerprints found at a crime scene.

DNA

• Investigators can extract DNA from almost any tissue, including hair, fingernails, bones, teeth and body fluids. The DNA is used to create a profile that can be compared to profiles from suspects or victims.

• CODIS (Combined DNA Index System) is a database maintained by the FBI that is used to find matches to unknown DNA samples from a crime scene.

Images: http://www.tcamb1.com/images/hairanalysis.jpg and http://www.npsg.uwaterloo.ca/resources/images/microscope/Sand%200004.jpg

Hairs & Fibers

• Hairs and fibers may be transferred from the suspect or the suspect’s clothes to the victims’ and vice versa. For example, a suspect may pick up carpet fibers on his shoes or leave hairs behind at a crime scene.

•  Hairs can be examined to identify their origin, such as human or animal. Hairs with roots intact can be tested for DNA.

• Fibers are used to make clothing, carpeting, furniture, beds, and blankets. They may be natural fibers from plants or animals or synthetic fibers that are man-made.

Dust & Dirt

• Dust, dirt, or sand evidence can reveal where a person has traveled and may be picked up at a crime scene or left behind.

• Investigators examine the samples for chemical composition, pollen, plant material, and other organic matter to find links to a specific crime scene.

Microscopic Image of Sand

Microscopic Image of Hairs & Fibers

Source: http://www.crime-scene-investigator.net/excavation.html Images: http://www.celticnz.org/images/Feedback/SkullSkeleton.JPG and http://www.legacyhealth.org/images/Housecalls/claviclefx.jpg

Skeletal Remains

• Forensic anthropologists analyze skeletal remains to determine four characteristics for a victim: age, sex, race, and stature (height/build).  Sex - Determined by examining the pelvis, humerus, and femur Age and stature – Determined by analyzing the development of the teeth, bone growth, and the length of specific bones, such as the femur. Race – Determined by analyzing the skull for characteristics that are common among people of different races.

• DNA samples can be collected from bone, teeth, and hair to provide clues to a person’s identity. Scientists may also be able to gain clues as to a person’s past, recent injuries, or the cause of death based on bone fractures and other signs of trauma.

Questioned Documents

• Examiners will analyze a ransom note or other document to find clues to link it to a crime scene or a specific suspect. They will analyze the type of paper used, printing method or handwriting style, and type of ink.

• Other unique features, such as watermarks on stationary or indentations made as someone wrote on a page in a notebook, may provide useful clues.

Wounds

• Wounds can often be matched to weapons or tool marks on the weapon. Investigators may also be able to determine the weapon's size, shape, and length. 

• Analysis of a wound may provides clues to a victim’s injuries, characteristics of the suspect (left-handed, right-handed, height, etc.), and positions of the victim and suspect at the time of the incident.

Mock Crime Scene: http://www.masss.gov

What evidence would you collect?