1. Chapter 3 3.1 Physical Evidence

2. OBJECTIVES (don’t write) Review the common types of physical evidence encountered at crime scenes, Explain the difference between the identification and comparison of physical evidence. Define and contrast individual and class characteristics of physical evidence. Give examples of physical evidence possessing these characteristics Discuss the value of class evidence as it relates to a criminal investigation.

3. Common Types of Physical Evidence 1. Blood, semen, saliva 2. Documents 3. Drugs 4. Explosives 5. Fingerprints 6. Firearms and ammunition 7. Glass 8. Hair 9. Impressions 10. Organs and physiological fluids 11. Paint 12. Petroleum products 13. plastic bags 14. Plastic, rubber and other polymers 15. Powder residues 16. Serial numbers 17. Soil and minerals 18. Tool marks 19. Vehicle lights 20. Wood and other vegetative matter

4. Significance of Physical Evidence Identification purpose determination of the physical or chemical identity of a substance with as near absolute certainty as existing analytical techniques will permit Process includes: a. adoption of testing procedures that give characteristic results for specific standard materials b. identification requires that the number and type of test needed to ID a substance is sufficient to exclude all other substances

5. Identification Used to determine chemical composition of drugs Identify gasoline residues in fire debris Identify blood, semen, hair, and wood to determine species of origin – i.e. human or animal

6. Significance of Physical Evidence Comparison purpose determination of whether or not there is a common origin suspect specimen and standard/reference specimen share same tests and examinations – i.e Hair samples, paint chips

7. Probability Odds at which a certain event will occur Blood types – type O blood is 0.5 – type A blood is 0.34 – B blood is 0.12. 2 identical Fingerprints = 1 x 10 60

8. Individual characteristics associated with common source matching ridge characteristics of two fingerprints comparison of random striation markings on bullets or tool marks comparison of irregular and random wear patterns in tire or footwear impression comparison of handwriting characteristics fitting together of the irregular edges of broken objects matching sequentially make plastic bags by striation marks running across the bags

9. Class Characteristics evidence that can be associated with a group and never a single source – Blood typing – Paint layers Product rules = formula for determining how frequently certain combination of characteristics occurs in a population

10. In-Class Assignment/Homework 3.1 Review Questions