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Chapter 3

Chapter 3. Physical Evidence. Common Types of Physical Evidence. Blood, semen & saliva Documents Drugs Explosives Fibers Fingerprints Firearms & ammunition Glass. Physical Evidence from A-Z. Hair Impressions Organs and physiological fluids Paint Petroleum products Plastic bags

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Chapter 3

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  1. Chapter 3 Physical Evidence

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

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

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

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

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

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

  8. Individual Characteristics • Properties of evidence that can be attributed to a common source with an extremely high degree of certainty • Victor Balthazard probability of 2 identical fingerprints is one in 1X 1060 See Examples on p. 66 Criminalistics

  9. Class Characteristics • Properties of evidence that can only be associated with a group and never with a single source • http://science.howstuffworks.com/forensic-lab-technique.htm/printable • (Video Forensic analysis of a gun) • http://videos.howstuffworks.com/science/fingerprint-videos-playlist.htm#video-3949 • The Black Hand Mob in NYC circa 1903

  10. Examples of Class Characteristics • Paint samples from a hit-and-run • Multiple layered samples increase the probability of “matching” a known sample • http://www.kcra.com/r/24405935/detail.html

  11. Examples of Class Characteristics • Blood • 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)

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

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