1. 3-1 PRENTICE HALL ©2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE An Introduction By Richard Saferstein PHYSICAL EVIDENCE Chapter 3

2. 3-2 PRENTICE HALL ©2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE An Introduction By Richard Saferstein Physical Evidence It would be impossible to list all the objects that could be of importance to a crime. Almost anything found at a crime scene can be Physical Evidence. It is difficult to predict the importance a given piece of evidence will have in a case as ultimately the evidence will be analyzed by a jury.

3. 3-3 PRENTICE HALL ©2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE An Introduction 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

4. 3-4 PRENTICE HALL ©2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE An Introduction 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 a suspect specimen and a standard/reference specimen to the same tests to show origin

5. 3-5 PRENTICE HALL ©2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE An Introduction By Richard Saferstein Identification Identification determines the physical or chemical identity as best as existing analytical technology will allow. –Identification requires the use of testing that have specific standards. –Identification requires that the tests establish the identify a substance to exclude all other substances.

6. 3-6 PRENTICE HALL ©2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE An Introduction 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, semen, hair, or wood and include the species origin.

7. 3-7 PRENTICE HALL ©2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE An Introduction 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.

8. 3-8 PRENTICE HALL ©2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE An Introduction 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

9. 3-9 PRENTICE HALL ©2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE An Introduction 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.

10. 3-10 PRENTICE HALL ©2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE An Introduction By Richard Saferstein Individual Characteristics Examples of Individual Characteristics –matching ridge characteristics of fingerprints -random striation markings on bullets -irregular and random wear patterns in tire or footwear impressions –handwriting characteristics –irregular edges of broken objects that fit together (like assembling a jigsaw puzzle) –matching marks on extruded sequentially made plastic bags

11. 3-11 PRENTICE HALL ©2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE An Introduction 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.

12. 3-12 PRENTICE HALL ©2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE An Introduction By Richard Saferstein More on Class Evidence When dealing with more than one type of class evidence, the entire group of evidence is used to show that they all came from the same source (from the same individual or manufacturer). The value of physical evidence is ultimately determined by the jury in court.

13. 3-13 PRENTICE HALL ©2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE An Introduction By Richard Saferstein Crossing Over Evidence that changes from class to individual presents requires more exacting proof: Number of striations are necessary to individualize a mark to a single tool. Number of color layers are needed to match a paint chip to one car? How many ridge characteristics are needed to match a fingerprint? How many handwriting characteristics tie a person to the samples? These are all questions that are addressed in court.

14. 3-14 PRENTICE HALL ©2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE An Introduction By Richard Saferstein Natural vs. Evidential Limits There are limits to the properties and characteristics the forensic scientist can select for comparison. –Modern analytical techniques have become so sophisticated and sensitive that naturally occuring variations in manufactured objects are almost unlimited. –Carrying natural variations to the extreme, no two things in this world are exactly alike in every detail. –Evidential variations are not the same as natural variations. –It is difficult to distinguishing evidential from natural variations.

15. 3-15 PRENTICE HALL ©2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE An Introduction 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.

16. 3-16 PRENTICE HALL ©2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE An Introduction 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.

17. 3-17 PRENTICE HALL ©2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE An Introduction By Richard Saferstein Reconstruction Reconstruction - the method used to support a likely sequence of events by using the notes/sketches and physical evidence. Crime-scene reconstruction relies on the combined efforts of medical examiners, criminalists, and law enforcement to sort out the events surrounding the occurrence of a crime.

18. 3-18 PRENTICE HALL ©2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE An Introduction By Richard Saferstein The Role of Physical Evidence The physical evidence left behind at a crime scene plays an important role in reconstructing the events that took place surrounding the crime. Although the evidence alone does not describe everything that happened, it can support or contradict accounts given by prosecution or the defense. Information obtained from physical evidence can also generate leads and confirm the reconstruction of a crime to a jury. The collection and documentation of physical evidence is the foundation of a reconstruction.

19. 3-19 PRENTICE HALL ©2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE An Introduction By Richard Saferstein Summing It Up Reconstruction is a team effort that involves putting together many different pieces of a puzzle. The right connections have to be made among all the parts involved so as to portray the relationship among the victim, the suspect, and the crime scene. If successful, reconstruction can play a vital role in aiding a jury to arrive at an appropriate verdict. The recognition, collection, and analysis of physical evidence is the foundation to successful reconstruction, but only part of the process.