CRJS 370 Criminalistics and Crime Analysis Notes Chapters 3-6.docx

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Criminal Justice
CRJS 370
Lindsey Wallace

Criminalistics and Crime Analysis Notes Chapters 3-6 Chapter 3 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. 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. Types of Physical Evidence -Blood, semen, saliva -Documents -Drugs -Fibers -Fingerprints -Firearms and ammunition -Glass -Hair -Impressions -Organs and physiological fluids -Paint -Petroleum products -Plastic bags Purpose of Examining Physical Evidence The exam of physical evidence by a forensic scientist is usually undertaken for ID or comparison purposes. ID has as its purpose the determination of the physical or chemical identity of a substance with as near absolute certainty as existing analytical techniques will permit. A comparison analysis subjects a subject specimen and a standard/reference specimen to the same tests and exams for the ultimate purpose of determining whether or not they have a common origin. Identification The objective of an ID is to determine the physical or chemical identity with as near absolute certainty as existing analytical techniques will permit. The process of ID first requires the adoption of testing procedures that give characteristic results for specific standard materials Once these test results have been established, they may be permanently recorded and used repeatedly to prove the ID of suspect materials Common Types of ID The crime lab is frequently requested to ID the chemical composition of an illicit drug It may be asked to identify gasoline in residues recovered from debris of fire Comparison A comparative analysis has the role of determining whether or not a suspect specimen and a standard specimen have a common origin Both are subjected to same tests Role of Probability To comprehend the evidential value of a comparison, one must appreciate the role that probability has in ascertaining the origins of 2 or more specimen Probability – frequency of occurrence of an event In flipping a coin, probability is easy to establish With many analytical processes, exact probability is impossible to define Classifying Characteristics Individual Characteristics Evidence that can be associated to a common source with an extremely high degree of probability is said to possess individual characteristics In all cases, it is not possible to state with mathematical exactness the probability that the specimens are of common origin It can be only concluded that this probability is so high as to defy math calculations or human comprehension -Two fingerprints -Random striation marks on bullets or tool marks -Irregular and random foot patterns -Handwriting characteristics -Putting pieces together in the manner of a jigsaw puzzle Class Characteristics Evidence associated only with a group Surprising to the inexperienced forensic scientist is the frequent inability of the lab to relate physical evidence to a common origin with a high degree of certainty Class Evidence(Problems and Weaknesses) Inability of the examiner to assign exact or even approximate probability values to the comparison of the most class physical evidence For example, what is the probability that a nylon fiber originated for a particular sweater, or that a paint chip came from a suspect in a hit and run There are very few statistical data available from which to derive this information The value of class evidence lies in its ability to provide corroboration of events with data that are, as nearly as possible, free of human error and bias When one is dealing with more than 1 type of class evidence, their collective presence may lead to an extremely high certainty that they originated from the same source Finally, the contribution of physical evidence is ultimately determined in the courtroom Crossing Over Crossing over the line from class to individual does not end the discussions 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? 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 Just as important, a person may be exonerated or excluded from suspicion if physical evidence collected at a crime scene is found to be different from standard/reference samples collected from that subject. Forensic Databases Integrated Automated Fingerprint ID System Combined DNA Index System National Integrated Ballistics Info Network International Forensic Automotive Paint Data Query Shoeprint Image Capture and Retrieval Forensic Pathology This field involves the investigation of sudden, unnatural, unexplained, or violent deaths The primary role of the medical examiner is to determine the cause of death If a cause cannot be found through observation, an autopsy is normally performed to establish the cause of death Forensic Pathologist = Medical Examiner Manner of death (5 categories) -Natural -Homicide -Suicide -Accident -Undetermined Estimating Time of Death Rigor Mortis – immediately after death, muscles relax and then become rigid, sets within 24 hours and disappears within 36 hours Livor Mortis – human hearts s
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