1. 3-1 ©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE: An Introduction, 2 nd ed. By Richard Saferstein PHYSICAL EVIDENCE Chapter 3

2. 3-2 ©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE: An Introduction, 2 nd ed. By Richard Saferstein Physical Evidence It would be impossible to list all the objects that could conceivably be of importance to a crime. Almost anything can be Physical Evidence. Although you cannot rely on a list of categories, it is useful to discuss some of the most common types of physical evidence.

3. 3-3 ©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE: An Introduction, 2 nd ed. By Richard Saferstein Physical Evidence The purpose of recognizing physical evidence is so that it can be collected and analyzed. It is difficult to ascertain the weight a given piece of evidence will have in a case as ultimately the weight will be decided by a jury.

4. 3-4 ©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE: An Introduction, 2 nd ed. By Richard Saferstein Examples of Physical Evidence Blood, semen, and saliva Documents Drugs Explosives Fibers Fingerprints Firearms and ammunition Glass Hair Impressions Organs and physiological fluids Paint Petroleum products Plastic bags Plastic, rubber, and other polymers Powder residues Soil and minerals Tool marks Vehicle lights Wood and other vegetative matter

5. 3-5 ©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE: An Introduction, 2 nd ed. By Richard Saferstein Examples of Physical Evidence Impressions – Tire markings, shoe prints, depressions in soft soils, and all other forms of tracks. Bitemarks in skin or food, are also included.

6. 3-6 ©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE: An Introduction, 2 nd ed. By Richard Saferstein Examining Physical Evidence The examination of physical evidence is done for two reasons: identification or comparison. Identification determines the physical or chemical identity Comparison subjects a suspect specimen and a standard/reference specimen to the same tests to show origin

7. 3-7 ©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE: An Introduction, 2 nd ed. By Richard Saferstein Identification Identification determines the physical or chemical identity as best as existing analytical technology will allow. –Identification requires that the tests establish the identify a substance to exclude all other substances.  Examples:  Identifying the composition of a drug  Identifying blood or hair from species of origin (human, dog, cat?)

8. 3-8 ©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE: An Introduction, 2 nd ed. By Richard Saferstein Evidence Identification The crime laboratory is frequently asked to identify: the chemical composition of an illicit drug. gasoline in residues recovered from arson debris explosive residues from bombs blood, hair, or wood and include the species origin.

9. 3-9 ©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE: An Introduction, 2 nd ed. By Richard Saferstein Comparison A comparative analysis determines whether a suspect specimen and a standard/reference specimen are the same Both the standard/reference and the suspect specimen are subject to the same tests. The forensic comparison is actually a two-step procedure: –Step One: Compare the standard/reference to the unknown specimen. –Step Two: Give a conclusion about where the specimen came from.

10. 3-10 ©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE: An Introduction, 2 nd ed. By Richard Saferstein Role of Probability Value of comparison depends on the probability of matching unknown specimens with known examples (controls/standards) Probability is the frequency of occurrence of an event. Ex: When flipping a coin, probability is easy to establish

11. 3-11 ©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE: An Introduction, 2 nd ed. By Richard Saferstein Classifying Characteristics Individual Characteristics –Evidence that can be linked to a single source with an extremely high degree of probability. Class Characteristics –Evidence linked to only a group of like objects.

12. 3-12 ©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE: An Introduction, 2 nd ed. By Richard Saferstein Individual Characteristics Examples of Individual Characteristics: –the matching ridge characteristics of two fingerprints –the comparison of random striation markings on bullets or tool marks –the comparison of handwriting characteristics –the comparison of irregular and random wear patterns in tire or footwear impressions –the fitting together of the irregular edges of broken objects in the manner of a jigsaw puzzle –matching sequentially made plastic bags by striation marks running across the bags

13. 3-13 ©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE: An Introduction, 2 nd ed. By Richard Saferstein Class Characteristics Class characteristics are associated with only a group (such as a manufacturing lot) and not a single source (such as one individual). Due to mass manufacturing matching to a specific company or lot is difficult.

14. 3-14 ©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE: An Introduction, 2 nd ed. By Richard Saferstein Determine whether the evidence is more likely to possess individual or class characteristics a.Impression from an automobile tire b.A fingerprint c.A spent bullet cartridge d.Pieces of a shredded document e.Commercial potting soil f.DNA g.Fragments of silver paint recovered from a Honda Accord Individual or Class Charact. a.Class characteristic b.Individual characteristic c.Individual characteristic d.Individual characteristic e.Class characteristic f.Individual characteristic g.Class characteristic

15. 3-15 ©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE: An Introduction, 2 nd ed. By Richard Saferstein Crossing Over Evidence that changes from class to individual Examples: -Number of striations are necessary to individualize a mark to a single tool. -Performing DNA profiling on a hair sample These are all questions that are addressed in court.

16. 3-16 ©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE: An Introduction, 2 nd ed. By Richard Saferstein Using Physical Evidence As the number of different objects linking an individual to a crime scene increases, so does the likelihood of that individual’s involvement with the crime/crime scene. Someone can also be exonerated (or excluded from suspicion) if the physical evidence collected at a crime scene is found to be different from the reference samples collected from that suspect.

17. 3-17 ©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE: An Introduction, 2 nd ed. By Richard Saferstein Forensic Databases The Integrated Automated Fingerprint Identification System (IAFIS), a national fingerprint and criminal history system maintained by the FBI. The Combined DNA Index System (CODIS) enables federal, state, and local crime laboratories to electronically exchange and compare DNA profiles. The National Integrated Ballistics Information Network (NIBIN) allows firearm analysts to acquire, digitize, and compare markings made by a firearm on bullets and cartridge casings. The International Forensic Automotive Paint Data Query (PDQ) database contains chemical and color information pertaining to original automotive paints. SICAR (shoeprint image capture and retrieval) is a shoeprint database.