1. Physical Evidence Chapter 3

2. Common Types of Physical Evidence

3. Identification To determine the physical or chemical identify of a substance – what is this? Examples: white powder, residues from debris of fire, hair etc. Comparison A comparison analysis subjects a suspect specimen and a control specimen to the same tests and examinations for the ultimate purpose of determining whether or not they have a common origin. Significance of Physical Evidence

4. Significance of Physical Evidence • The probability that the specimen came from the crime scene must always be considered. See Page 104 in text for glass refractive indexes as an example.

5. Individual Characteristics When evidence can be associated with a common source with an extremely high degree of probability; unique Class Characteristics When evidence can be associated with a group and never with one single source; used to place a suspect at a scene Significance of Physical Evidence

6. Significance of Physical Evidence • Examples of Class vs Individual Characteristics • Blood ABO type is class • DNA is individual • Shoe impression would be class • If the shoe impression has specific wear marks it can be considered individual

7. Significance of Physical Evidence • Combination of many different pieces of class evidence raises the probability of an event • Physical evidence can be used to eliminate a suspect. • When does evidence pass from class to individual status?

8. Significance of Physical Evidence Crime Scene Reconstruction • Purpose: supports the likely sequence of events by the observation and evaluation of physical evidence, as well as witness statements. • Often involves medical examiner, analysis of blood spatter, determining direction and distance from shooting source; GSR