Chapter 3 Evidence

What is Evidence?

Something that tends to establish or disprove a fact. Evidence can include documents, testimony, and other objects

2 Types of Evidence *Testimonial * Physical

Testimonial Evidence What is said in court by a competent witness or a statement made under oath Also called direct evidence or “prime facie” * “That’s the guy I saw robbing the grocery store”

Tangible items that tend to prove some material fact; Physical Evidence Tangible items that tend to prove some material fact; this is also called Real Evidence

Every crime scene obviously has to be treated on an individual basis, having it’s own peculiar history, circumstances, and problems.

A qualified evidence collector can not rely on collection procedures memorized from a pamphlet, but they must be able to make innovative, on-the-spot decisions at the crime scene.

Common types of Physical Evidence Blood, semen, saliva Documents Drugs Explosives Fibers Fingerprints Firearms and ammunition Glass Hair Organs and physiological fluid Vehicle lights Impressions Paint Petroleum products Plastic bags Plastic, rubber, other polymers Powder residues Serial numbers Soil and minerals Tool marks Wood and other vegetate matter

Not all evidence is permanent: Transient Evidence *odors – perfume, purification, gasoline, cigarette smoke *temperature – coffee pot, car hood, dead body *imprints and indentations – footprints in sand, fingerprints in dust, teeth marks in perishable foods

Conditional Evidence Produced by specific action or event at the scene that must be observed and documented: *lights on or off * garage door up or down *doors open or closed *position of body and the furniture

Evidence providing only a basis for inference about the fact. Indirect Evidence Evidence providing only a basis for inference about the fact.

Circumstantial Evidence Implies fact or event without actually proving it. -Evidence based on suggestion rather than personal knowledge or observation.

Identify Compare Significance of Physical Evidence Why do Forensic Scientists examine evidence? Identify Compare

Identification The process of determining a substance’s physical or chemical identity.

Look at physical and chemical properties *color *density * solubility *hardness *refractive index Chemical * bubbles *color change *pH change *formation of precipitate

Process of Identification A – Adoption of testing procedures that give characteristic results for specific standard materials B – Requires that the number and type of tests needed to identify a substance be sufficient to exclude all other substances Ultimately, the conclusion will have to be substantiated beyond any reasonable doubt in a court of law.

Comparison The process of ascertaining whether two of more objects have a common origin

Forensic Comparison 1st – combination of select properties are chosen from the suspect and the standard/ reference specimen for comparison 2nd – once examination completed forensic scientist must be prepared to render a conclusion with respect to the origins of the specimens.

Questioned or Unknown Sample Material that has been collected from a known location but is of unknown origin *paint on bumper of a vehicle that is suspected to have been involved in a hit and run

Known Sample Material that comes from a proven of known source *compared to paint from the victims bicycle

Control Sample Material that is similar to the question and know samples, and is used to validate the test method and procedure

Individual vs. Class Evidence

Individual Evidence Material that can be related to a single source; individualization always involves a comparison *fingerprints *handwriting *DNA patterns *broken glass that fits exact; like a puzzle

Class Evidence Material that can be associated only with a group of items that share properties of characteristics Example: a pair of blue jeans

Probability The frequency of occurrence of an event To comprehend the evidential value of a comparison, one must appreciate the role that probability has in ascertaining the origins of two or more specimens. (p.65)

Individual characteristics have an extremely high degree of probability. Victor Balthazard determined probability of 2 people having the same fingerprints to be 1X10 to the 60th. That is 100000000000000000000000000000000000000000000000000000000000

Class Characteristics of evidence provide more weight as the probability goes up. Example given: paint chip from a car with 1 layer of paint versus a paint chip with 7 layers of paint.

Product Rule Multiplying together the frequencies of independently occurring genetic markers to obtain an overall frequency of occurrence for a genetic profile. Example given: Blood factors (p.67)

Crime Scene Reconstruction All professionals contribute a unique perspective to develop the crime-scene reconstruction. Reconstruction: the method used to support a likely sequence of events by the observations and evaluation of physical evidence, as well as statements made by those involved with the incident. (p.70)