Physical Evidence Types of Physical Evidence n Blood

Physical Evidence

Types of Physical Evidence n Blood, Semen, Saliva n Documents n Drugs n Explosives n Fibers n Fingerprints n Firearms and ammunition

More types… n Glass n Hair n Impressions (tires, shoes, any tracks) n Organs and Physiological fluids – these are needed to be tested for detection of drugs or

Even more… n Paint n Petroleum products n Plastic bags – prints or transfer…garbage bags n Polymers n Powders n Serial numbers n Soil and minerals

You should get the idea now… n Tool marks n Vehicle lights – my downfall n Wood and vegetative matter – plant DNA!!! n What does the length of this list tell you about a crime scene investigation?

Purpose of Physical Evidence n IDENTIFICATION n COMPARISON

Identification n Determination of the physical or chemical identity of a substance with as near absolute certainty as existing techniques will permit n The analyst must determine a scheme in order to rule out all but one of the samples

Comparison n Subjects a suspect specimen and a control specimen to the same tests and examinations in order to determine a common origin n PLACE SCENE THEM AT THE

Individual vs. Class Characteristics n Individual characteristics are characteristics that can be associated with a common source to a high degree of probability n Examples: bullet striations and tool marks, ridge detail, wear patterns on impressions, handwriting, irregular fits for broken objects n Possibility of two people having the same fingerprints is 1 in 1000000000000000000000000000 or 1 in 1 x 1060

n Class Characteristics – physical evidence with a common origin. This evidence can only be associated with a group and or never a single source n n Examples: 2 layer car paint vs. 7 layer paint, Type A blood (26% of population) OJ example Blood factors present: A (26%), Es. D 1 (85%), and PGM 2+2 - (2%) n This equates to a. 44% (1 in 200) chance it was OJ’s blood n

Weaknesses n It is hard to establish probabilities with many types of physical evidence as most type are class evidence. n How does our industry and economy affect this? n If this is the case, then what is the value of class evidence?

Crime Scene Reconstruction n Requires: n n Law enforcement personnel, medical examiner, and criminalists Questions to ask: How many people were involved? n How was the victim killed? n Was there a cover-up? n n Reconstruction supports a likely sequence of events by the observation and evaluation of physical evidence and statements by witnesses or those involved.