Evidence Chapter 2

2 types of evidence: Testimonial Evidence: Physical Evidence Statement made under oath Physical Evidence Any object or material relevant in a crime Tangible Direct/Indirect Class/Individual

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 reduce accuracy of eye witness: Length of time of encounter Darkness/ distance Stress: weapon diverts attention Time between event and questioning New info can affect memory Read about case Look at mug shots Leading questions “was the offenders shirt red?” instead of “what was the offender wearing?”

Studies show: Witnesses are more accurate at noting suspects: Sex hair color Witnesses are less accurate with noting suspects: age, height, specific race A witness is more accurate if suspect is physically similar to themselves

Make good witnesses: middle-aged 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 fire Back up/refute witness testimony Link suspect to crime scene; prints at scene I.D. people that were there Reconstruct the crime In general, physical evidence is more reliable than testimonial evidence.

Known/Control sample:material that comes from a proven or known source Questioned/Unknown sample: found at crime scene Example: find fingerprint at crime scene, compare it with all KNOWN prints through AFIS.

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.

Circumstantial Evidence Evidence based on suggestion rather than personal knowledge or observation, more you have, the better Example: A blond hair is found in hand of a murder victim with black hair. Circumstantial because there are many blonds. If a footprint size 11 was also found, it is circumstantial Put them together and you limit the pool of suspects

Individual vs. Class Evidence Individual Evidence: evidence that can be traced to one source DNA, fingerprints, broken glass or paper that fits like puzzle. Class Evidence: can be classified into a group. black hair, white shirt, denim pants

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

The product rule: The more class evidence you have the useful it becomes.

Probative value 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!

Probability Product rule for the probative value of class evidence. Suspect wearing white shirt, blue pants, Light brown hair

Class to Whole population 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.

Sample population to whole Blue pants Say 15/30 in this class = .5 .5 x 1200 = 600 in the school wearing blue pants

Sample population Light brown hair 15/30 = .5 .5 x1200 = 600 students in school with light brown hair

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

The Product Rule .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

The Product Rule .333 x .5 x .5 = .0825 .0825 x 1200 = 100 Narrowed school population down to 100 possible suspects with all 3 criteria