September 2, 2014 Physical Evidence Introduction to Physical Evidence Recognize, Collect, & Preserve The roles of Physical Evidence: 1. Reconstruct the Crime Scene & Sequence of Events 2. Determine whether or not a crime occurred. 3. Link an individual with another or with a crime scene 4. Provide Investigative Leads to Investigators. 5. Provide facts to a jury which may assist in the determination of the guilt or innocence of an accused. 6. Provide evidence to link serial homicide or rape case. Advantages of Physical Evidence ? Provides a tangible object for the jury to see ? Can be taken into the jury room ? The defendant cannot distort the physical evidence. ? Some cases cannot be solved without the physical evidence ? Physical evidence is not subject to memory loss ? The defendant can have the evidence tested by an independent expert. Evidence ? Anything ? Materials collected and scientifically analyzed to determine the nature and circumstances of a crime. ? Direct ? establishes a fact (eyewitness) ? Circumstantial ? provides an inference about what happened (more reliable than direct) Evidence Analysis Identification Comparison ? Determine the physical or chemical identity of a substance ? Answer the question: ?What is it?? ? Suspect and standard specimens ? Answer the question: ?Does it Match?? Physical Evidence Characteristics Class Characteristics Individual Characteristics ? Intentional or recurring characteristics ? Evidence associated with one group ? Unintentional, random, and unique features ? Evidence associated with common source with high degree of probability Probability ? The frequency of occurrence of an event. ? In all cases, it is not possible to state with mathematical exactness the probability that the specimens are of common origin. ? It can only be concluded that this probability is so high as to defy mathematical calculations or human comprehension. Class Evidence ? Inability to assign exact or even approximate probability values to the comparison of most class physical evidence. ? Currently trying to update statistical databases for class evidence ? Value of class evidence ? Corroboration ? Additive probability From Class to Individual Evidence ? 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? Identifying Physical Evidence ? Presumptive Tests ? Identify suspect evidence (class) ? Cheaper ? Faster ? Can be done at crime scene ? Less training needed ? Help focus investigation ? Specific Tests ? Can lead to individual classifications ? Costly ? Time consuming ? Typically done in the lab ? More exact procedure ? Match a suspect to a crime Six Types of Evidence Trace evidence Locard?s exchange principle Indented or impression evidence Transfer evidence Striated evidence Geometric evidence Chemical evidence 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. Reconstruction and Physical Evidence Any Questions? Adrienne PowerPoint Presentation
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