Forensic Crime Scene Analysis



CRJ 311: Forensic ScienceLecture 3 - Physical EvidenceValue of Physical and Trace EvidenceMany police shows depict eyewitness evidence as being most important to solving cases.How reliable and important is eyewitness evidence?Physical EvidenceAs noted in Chapter 2, the purpose of recognizing physical evidence is so that it can be collected, packaged and transported properly for analysis in a crime lab.What did Chapter 2 identify as physical evidence?Can almost anything be classified as physical evidence?Other than DNA, blood, hair and fibers, what other types of physical evidence would CSI look to collect?Common Types of Physical EvidenceBlood, semen and salivaDocumentsDrugsExplosivesFibersFingerprintsFirearms and ammunitionGlassHairImpressionsOrgans and physiological fluidsPaintPetroleum productsPlastic bagsPlastic, rubber and other polymersPowder residuesSoil and mineralsTool marksVehicle lightsWood and other vegetative matterSignificance of Physical EvidenceThe examination of physical evidence by a forensic scientist is usually undertaken for the following:Identification:Comparison Analysis:IdentificationThe process of identification requires the following:First:Example:Second:Does it require several tests?Identification “Other Examples”Listed below are common types of identification in the crime laboratory:Comparative Analysis “2-Step Process”Determine whether a specimen and standard have a common origin.Are the standard/reference and suspect specimen subject to the same tests?Comparative analysis is a 2-step process:First:Second:Comparative Analysis “SICAR: Shoeprint Database”Who was the “Night Stalker”?How were his shoes useful?Why are databases useful in today’s cases?Comparative Analysis “The Role of Probability”Probability is very important to evidence. What does it mean?Probability:Flipping a coin:DNA:Comparative Analysis “Classifying Characteristics”Individual Characteristics:Class Characteristics:Comparative Analysis “Individual Characteristics”In all cases, it is not possible to state with mathematical exactness the probability that a specimens are of common origin.How do we conclude?Examples:Comparative Analysis “Class Characteristics”The crime laboratory has a frequent inability to relate physical evidence to a common origin with a high degree of certainty.What evidence is said to possess class characteristics?Example:Challenges with Class Evidence ComparisonOne of the current weaknesses in forensic science is the inability of the examiner to approximate probability values to the comparison of most class physical evidence.What is the probability that a nylon fiber originated from a particular sweater?It is not like CSI on TV!The Solution to Class Evidence Comparison ChallengeForensic scientists create and update statistical databases for evaluating the significant of class physical evidence.Can evidence be linked to a single person at a crime scene?What is the value of class physical evidence?Do databases allow for “crossover” from class to individual comparisons?“Crossing Over” Still Leaves Questions“Crossing Over” the line from class to individual does not end the discussions.These remaining questions defy simple answers and are the basis of continued arguments:Using Physical EvidenceAs the number of different objects linking an individual to a crime scene increases, so does the likelihood of what?Can a person be exonerated or excluded from evidence collected at the crime scene? How?Forensic DatabasesAutomated Fingerprint Identification System (AFIS):Combined DNA Index System (CODIS):National Integrated Ballistics Information Network (NIBIN):International Forensic Automotive Pain Data Query (PDQ):SICAR:Crime Scene ReconstructionThe method used to support a likely sequence of events by the observation and evaluation of physical evidence, as well as statements made by those involved with the incident.Who is involved in crime scene reconstruction?SUMMARY Role of Physical EvidenceThe physical evidence left behind at a crime scene plays a crucial role in reconstructing the events that took place surrounding the crime.Video: Richard RamirezWhat evidence was crucial to his arrest?What other evidence may have been important? ................
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