Chapter 3 Physical Evidence

Common Types of Physical Evidence Blood, semen & saliva Blood, semen & saliva Documents Documents Drugs Drugs Explosives Explosives Fibers Fibers Fingerprints Fingerprints Firearms & ammunition Firearms & ammunition Glass Glass

Physical Evidence from A-Z Hair Hair Impressions Impressions Organs and physiological fluids Organs and physiological fluids Paint Paint Petroleum products Petroleum products Plastic bags Plastic bags Plastic, rubber, and other polymers Plastic, rubber, and other polymers Powder residues Powder residues Serial numbers Serial numbers Soil and minerals Soil and minerals Tool marks Tool marks Vehicle lights Vehicle lights Wood and other vegetative matter Wood and other vegetative matter

Identification vs. Comparison Identification Identification the process of determining the physical or chemical identity of a substance the process of determining the physical or chemical identity of a substance What are some examples? What are some examples?

Examples of Physical Evidence to be identified Drugs, species determination, explosive residue Drugs, species determination, explosive residue

Drug Analysis Australian Federal Police via GettyGetty Images Images Forensic technicians are often called to identify unknown drugs. A beauty student allegedly tried to smuggle more than 10,000 amphetamine tablets into Australia.

Comparison Determining whether 2 or more objects have a common origin Determining whether 2 or more objects have a common origin What is required? What is required? A standard/reference sample A standard/reference sample Results may be reported as probability (frequency of occurrence of an event) Results may be reported as probability (frequency of occurrence of an event)

Individual Characteristics Properties of evidence that can be attributed to a common source with an extremely high degree of certainty Properties of evidence that can be attributed to a common source with an extremely high degree of certainty Victor Balthazard probability of 2 identical Victor Balthazard probability of 2 identical fingerprints is one in 1X See Examples on p. 66 Criminalistics See Examples on p. 66 Criminalistics

Class Characteristics Properties of evidence that can only be associated with a group and never with a single source Properties of evidence that can only be associated with a group and never with a single source technique.htm/printable technique.htm/printable technique.htm/printable technique.htm/printable (Video Forensic analysis of a gun) (Video Forensic analysis of a gun) playlist.htm#video playlist.htm#video playlist.htm#video playlist.htm#video-3949 The Black Hand Mob in NYC circa 1903 The Black Hand Mob in NYC circa 1903

Examples of Class Characteristics Paint samples from a hit-and-run Paint samples from a hit-and-run Multiple layered samples increase the probability of “matching” a known sample Multiple layered samples increase the probability of “matching” a known sample

Examples of Class Characteristics Blood Blood Blood type alone may not be a basis to establish common origin Blood type alone may not be a basis to establish common origin Product Rule- multiplying together the frequencies of independently occurring genetic markers to obtain an overall frequency of occurrence for a genetic profile (see p. 67) Product Rule- multiplying together the frequencies of independently occurring genetic markers to obtain an overall frequency of occurrence for a genetic profile (see p. 67)

Who decides? The weight or significance of physical evidence in a case is usually left to the jury. The weight or significance of physical evidence in a case is usually left to the jury.