3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein 1 Chapter 3 PHYSICAL EVIDENCE

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein 2 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 Appreciate the value of class evidence as it relates to a criminal investigation List and explain the function of national databases available to forensic scientists Explain the purpose physical evidence plays in reconstructing the events surrounding the commission of a crime Objectives

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein 3 awcnMrZiSmU&feature=related

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein 4 Physical Evidence Impossible to list all the objects of importance to a crime Almost anything physical evidence Discuss some of the most common examples –Collected and analyzed –Weight unknown for given piece of evidence –Decided by a jury

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein 5 Types of Physical Evidence Blood, semen, and saliva Documents Drugs Explosives Fibers Fingerprints Firearms, 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

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein Group the types of physical evidence into groups base on type 6

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein Key Points Biological crime scene evidence includes blood, saliva semen, DNA, hair, organs Impression crime scene evidence includes tire markings, shoe prints depressions in soft soil, all other forms of tracks, glove and other fabric impressions, tool mark and bite marks Manufactured items include firearms, ammunition fibers paint glass petroleum product plastic bags rubber polymers 7

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein 8 The Examination of Physical Evidence Identification or comparison purposes

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein 9 Identification Items from the body for laboratory examination Determine the physical or chemical identity Near absolute certainty as existing analytical techniques will permit Requires the adoption of testing procedures –Give characteristic results –Specific standard materials

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein 10 Identification Once test results have been established: –May be permanently recorded and used repeatedly to prove the identity of suspect materials. Number and type of tests needed to identify a substance: sufficient to exclude all other substances.

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein 11 Common Types of Identification Chemical composition of an illicit drug Gasoline in residues recovered from the debris of a fire Nature of explosive residues Blood, semen, hair, or wood Species origin

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein 12 Comparison Important role of determining common origin. Both the standard/reference and the suspect specimen subject to the same tests Two-step procedure –Combinations of select properties chosen –Forensic scientist renders conclusion

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein 13 Classifying Characteristics Individual Characteristics Class Characteristics

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein 14 Individual Characteristics Not possible to state with mathematical exactness the probability that the specimens are of common origin Only be concluded that this probability is so high as to defy mathematical calculations or human comprehension

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein 15 Individual Characteristics Ridge characteristics of two fingerprints Random striation markings on bullets or tool marks Irregular and random wear patterns in tire or footwear impressions

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein 16 Individual Characteristics Handwriting characteristics Irregular edges of broken objects in the manner of a jigsaw puzzle Sequentially made plastic bags by striation marks running across the bags

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein 17 Class Characteristics Frequent inability of laboratory to relate physical evidence to a common origin with a high degree of certainty Class characteristics –Associated only with a group –Never with a single source Probability is determining factor High diversity of class evidence in our environment Comparison very significant in context of a criminal investigation

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein 18 Class Evidence Weakness: inability of the examiner to assign exact or even approximate probability values to comparison of most class physical evidence Examples –Nylon fiber originated from a particular sweater –Paint chip came from suspect car in a hit and run Few statistical data available from which to derive this information Gathering this kind of data is elusive

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein 19 Class Evidence Create and update statistical databases Most items of physical evidence –Cannot be linked definitively to a single person or object The value of class physical evidence –Ability to provide corroboration of events with data –Free of human error and bias

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein 20 Class Evidence Chances are low –Encountering two indistinguishable items of physical evidence at a crime scene –Actually originated from different sources More than one type of class evidence –Collective presence may lead to an extremely high certainty that they originated from the same source Contribution of physical evidence is ultimately determined in courtroom

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein 21 Role of Probability Probability: frequency of occurrence of an event Flipping a coin Analytical processes: exact probability impossible

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein 22 Crossing Over Crossing over the line from class to individual How many striations are necessary to individualize a mark to a single tool and no other? How many color layers individualize a paint chip to a single car? How many ridge characteristics individualize a fingerprint? How many handwriting characteristics tie a person to a signature?

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein 23 Using Physical Evidence Number of different objects linking an individual to a crime scene  Likelihood of that individual’s involvement with the crime  Person may be exonerated or excluded from suspicion –Physical evidence collected at crime scene is found different from standard/reference samples collected from subject

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein Key Points The value of class evidence lies in its ability to corroborate events with data in a manner that is free of human error 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 A person maybe exonerated from suspicion if physical evidence collected is found to be different form standard/reference samples 24

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein 25 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.

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein 26 Forensic Databases 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.

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein 27 Forensic Databases SICAR (shoeprint image capture and retrieval) is a shoeprint database.

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein 28 Reconstruction Method used to support a likely sequence of events –Observation and evaluation of physical evidence –Statements made by those involved with incident Relies on the combined efforts of –Medical examiners –Criminalists, –Law enforcement personnel Recover physical evidence Sort out the events surrounding the occurrence of a crime

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein 29 Figure 3–6 A laser beam is used to determine the search area for the position of a shooter who has fired a bullet through a window and wounded a victim. The bullet path is determined by lining up the victim’s bullet wound with the bullet hole present in the glass pane.

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein 30 Role of Physical Evidence Crucial role in reconstructing the events that took place surrounding the crime Does not describe everything that happened Supports or contradicts accounts given by witnesses and/or suspects Generates leads Confirms the reconstruction of a crime to a jury. Foundation of a reconstruction

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein vocabulary class characteristics Properties of evidence that can be associated only with a group and never with a single source. comparison The process of ascertaining whether two or more objects have a common origin. identification The process of determining a substance’s physical or chemical identity 31

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein individual characteristics Properties of evidence that can be attributed to a common source with an extremely high degree of certainty. product rule A formula for determining how frequently a certain combination of characteristics occurs in a population. The product rule states that one must first determine the probability of each characteristic occurring separately, then multiply together the frequencies of all independently occurring characteristics. The result is the overall frequency of occurrence for that particular combination of characteristics. 32

3 - PRENTICE HALL ©2007 Pearson Education, Inc. Upper Saddle River, NJ CRIMINALISTICS An Introduction to Forensic Science, 9/E By Richard Saferstein reconstruction The method used to support a likely sequence of events at a crime scene by observing and evaluating physical evidence and statements made by those involved with the incident. 33