PHYSICAL EVIDENCE Class Notes 2 TYPES OF EVIDENCE

PHYSICAL EVIDENCE Class Notes

2 TYPES OF EVIDENCE • 1) Testimonial • 2) Physical

TESTIMONIAL EVIDENCE • Testimonial evidence is a statement under oath. • It is also called direct evidence.

TESTIMONIAL EVIDENCE • Eyewitnesses can provide important evidence in leading to an arrest. • However, eyewitnesses are not always reliable.

TESTIMONIAL EVIDENCE • Things police need to consider when determining if an eye witness is reliable: • 1) Type of crime and how the witness saw it. • People tend to be more accurate with sex and hair color than age, height and specific race.

TESTIMONIAL EVIDENCE • 2) Victims of serious crimes tend to have a more accurate memory. • If a weapon was used, it is usually remembered.

TESTIMONIAL EVIDENCE • 3) Some witnesses have a better memory than others. • Typically children and older adults don’t remember as well as others.

TESTIMONIAL EVIDENCE • 4) Interviewing techniques or how information is retrieved can make a difference in accuracy.

TESTIMONIAL EVIDENCE • 5) Open ended questions often get better answers. • Police should never ask leading questions such as “was the offenders shirt red? ”

TESTIMONIAL EVIDENCE • Other things to think about: • 1) Does the witness know the accused and what has their relationship been? • 2) How much time has passed since the crime? • 3) Has the witness identified the defendant? • 4) Have they already implemented someone else in the crime?

PHYSICAL EVIDENCE • It the task of the Forensic Scientist to look at evidence and determine its identity and its origin. • Physical and Chemical properties must be noted.

PHYSICAL EVIDENCE • Physical properties include color, density, solubility, hardness and refractive index.

PHYSICAL EVIDENCE • Chemical properties include production of gases, color change, p. H change and the formation of a precipitate.

PHYSICAL EVIDENCE Common Types Of Physical Evidence Drugs and toxic substances Resins, plastics fingerprints paints Explosive residues hair Gunshot residues Serial numbers tissues Firearms and ammunition documents pollen impressions fibers Wood material Petroleum products soil feathers alcohols glass bones Rubber materials Blood and bodily fluids Tool marks

TRANSIENT EVIDENCE • Transient evidence is easily changed or lost. • Example: Odors of perfume, gasoline, cigarette smoke; footprints in sand, temperature of items.

CONDITIONAL EVIDENCE • Conditional evidence is produced by an action. • Example: Doors opened or closed, lights on or off.

INDIRECT VS CIRCUMSTANTIAL EVIDENCE • Indirect evidence does prove a fact. • Circumstantial evidence implies a fact or event without proving it. • Example: Size 11 footprint found at crime scene

VALUE OF PHYSICAL EVIDENCE • 1) Can prove a crime has been committed and set the scene for the investigation. • 2) Can back up witness testimony or prove it false. • 3) Can link a suspect with a victim or crime scene. • 4) Can determine the identity of a suspect. • 5) Can allow investigators to reconstruct a crime scene.

VALUE OF PHYSICAL EVIDENCE • Once physical evidence is collected an unknown sample is compared to a known sample. • A control sample refers to a material that is expected to respond in a particular way in testing.

SIGNIFICANCE OF PHYSICAL EVIDENCE: INDIVIDUAL VS CLASS • Individual evidence is the best evidence because it can be linked to a unique, single, specific source. • Example: Fingerprints, DNA

SIGNIFICANCE OF PHYSICAL EVIDENCE: INDIVIDUAL VS CLASS • However, most evidence is class evidence. This evidence is common to a group of similar objects, but not to one single object. • Example: tennis shoes