Testimonial Physical

◦ Direct/indirect◦ Class/individual

Direct Evidence:◦ Needs no interpretation◦ Testimonial evidence: testified to under oath◦ Physical evidence: ie. DNA or Fingerprints

Indirect evidence:◦ Does not directly prove something◦ Physical evidence: strand of hair, car LIKE yours

Example: Direct evidence: drugs on a person proves

possession.

Example: Indirect evidence: wad of money on

person….suspect drug sales.

Testimonial evidence:◦ Testified to under oath (usually in the court)

◦ Studies show 80% conviction rate in cases with eyewitness.

◦ Most known cases of wrongful conviction involved an eye witness.

Things that diminish accuracy of eye witness:◦ Brevity of encounter◦ Darkness/ distance◦ Stress: weapon diverts attention◦ Time between event and questioning◦ New info. Can effect memory

Read about case Look at mug shots Leading questions

Studies show: Witness more accurate at noting suspects:

sexhair color

Witness less accurate with noting suspects: age, height, specific race

Witness is more accurate if suspect is Similar to witness

Make good witnesses: middle age

Make poor witnesses: ◦ Elderly◦ Young children◦ Alcohol or drug users◦ Head injury

Physical evidence:◦ Can be direct or indirect◦ Any object or material:

Microscopic: DNA, particles in soil Macroscopic: hair, finger print, blood odor

Physical Evidence can be used to:Prove a crime was committed; gas at fireLink suspect to crime scene; prints at sceneI.D. people that were thereReconstruct scene

Exemplar: the known or control group

Unknown: found at crime scene. Example: find fingerprint at crime scene,

compare it with all KNOWN prints through afis.

Individual Evidence: evidence that can be traced to 1 source. Ex; DNA, fingerprints, broken glass or paper that fits like puzzle.

Class Evidence: can be classified into a group. Ex; black hair, white shirt, denim pants

Does class evidence have any value? What kind of evidence is most common? Are most criminals smart?

Classes of objects can be progressively narrowed by looking at successively more traits

Results in continually fewer objects being classified as similar to each other

If the traits being compared are not unique to the source◦ item will possess traits that might be shared

with a wide variety of sources

Cocaine in a container can be identified as cocaine by its chemical properties

These properties are shared by all samples of the same molecular structure

Cocaine from Columbia looks just like cocaine from any commercial source

Sometimes (particularly in drug cases) identification of the evidence item is all that is required

The source of the cocaine is not important◦ its possession is illegal

White cotton fibers are so common that they will be present in almost all trace evidence collection

Fiber can be identified as cotton via polarizing light microscope

Origin from a specific source can’t be determined without looking at some non-cotton characteristic such as trace elements

Discovery of fibers that fall into the class of white cotton not very useful

A bullet can be identified as .22 caliber by measurement

May be isolated to a specific manufacturer by its markings

Manufacture usually produces millions of rounds of such ammunition◦ can’t distinguish one round from another by

looking only at caliber Firearms examiner would look at

individualizing characteristic such as bullet striae to increase the probative value

The product rule: The more class evidence you have the

useful it becomes.

The worth/value of evidence in court Example….soil or red paint on jeans

not very valuable…..both on 1 pair of jeans and both match soil/paint at crime scene!

Product rule for the probative value of class evidence.

Suspect wearing white shirt, blue pants. Light brown hair

How many kids in this class wearing white shirt

Say 10/30 =.333

Whole school population 1200 1200 x .333 = 400 kids in school wearing

white shirt.

Blue pants Say 15/30 in this class = .5

.5 x 1200 = 600 in the school wearing blue pants

Light brown hair 15/30 = .5

.5 x1200 = 600 students in school with light brown hair

How do you estimate how many kids in the Whole school are wearing white shirts and blue pants and light brown hair

.333 (1/3) of kids in this class are wearing white shirts.

.5 (1/2) of kids in this class are wearing blue pants

.5 (1/2) of kids in this class have light brown hair

.333 x .5 x .5 = .0825

.0825 x 1200 = 100

Narrowed school population down to 100 possible suspects with all 3 criteria