Physical Evidence - Pequannock Township High School
Physical Evidence Definition Physical evidence consists of tangible articles found at a crime scene that can be introduced in a trial to link a suspect or victim to the scene Physical Evidence Analysis
and interpretation can provide different types of information including: 1. Information on the Corpus Delicti the body of the crime essential facts which show that a crime has taken place 2. Information on the Modus Operandi characteristic of Physical Evidence
Linking a suspect with a victim Locards Exchange Principle blood, hairs, clothing fibers, and cosmetics can be transferred between victim and suspect 4. Linking a person to a crime scene fingerprints, blood, hairs, fibers, soils, bullets etc. 3. Physical Evidence Disproving or Supporting a Witnesss Testimony analysis
can indicate whether a persons version of a set of events is credible or whether the person might be lying 6. Identification of a suspect The best evidence for identifying a suspect is either fingerprints or body fluid (specifically blood/semen) 5. 7.
Providing Investigative Leads can help direct an investigation along a productive path Example: in a hit-and-run case a chip of paint from the vehicle can be used to narrow down the number and kinds of different cars that may have been involved Physical Evidence
Trace evidence piece of physical evidence that can be used to identify or link a suspect to a crime Trace evidence includes physical evidence as well as chemical and biological evidence
What is Trace Evidence? Remember Locards Exchange Principle? Every contact results in a transfer of evidence Purpose of Physical
Evidence Physical evidence is examined for identification or comparison purposes Identification the process of determining a substances physical or chemical identity Comparison the process of determining whether two or more objects have a common origin
Identification Examples Chemical composition of substances that illicit drugs Residue from a fire or explosion Identification of blood, semen, or wood Comparison Examples A
hair found at a crime scene may match a hair sample taken from a suspect A paint chip found on a hit and run victims clothing may match paint taken from a suspects vehicle Comparison Characteristics 2 types of comparison
characteristics: Individual Class Individual Characteristics Evidence that can be associated to a common single source with an extremely high degree of probability Never 100% certain High degree of probability
Individual Characteristic Examples Fingerprints Striation markings on bullets or tool marks Wear pattern in foot and tire prints Handwriting characteristics The fitting together of the irregular edges of broken objects as in a jigsaw
puzzle Matching sequentially made plastic bags by striation marks running across the bags Class Characteristics Evidence that can be associated only with a group and not with a single source Examples: Blood types
Paint from a car Clothing fibers Carpet fibers Scenario A student is kidnapped on the way home from school. Her backpack is found on the side of the road. There are several strands of hair caught in the zipper. Is this individual or class evidence? Explain why.
Scenario A victim tore a lock of blonde hair from her attacker. Is the hair class or individual evidence? Scenario Fingerprint evidence is
recovered from a breaking and entering crime scene. Is this class or individual evidence? Scenario DNA is extracted from blood that was left behind when a
perpetrator broke through a window. Is DNA class or individual? Scenario A victim reports a mugger was wearing a white t-shirt and police are holding a suspect wearing a white t-shirt. Is the t-shirt class or individual evidence?
Comparison Substantial part of the work in a forensic analysis consists of making comparisons between questioned (Q) and known (K) samples Outcomes 3 possible outcomes when Q and
K samples are compared: They match They do not match Insufficient sample to make a conclusive comparison Classification of Physical Evidence 7 schemes for classifying physical evidence Type of crime
Type of material General nature of evidence Physical state of evidence Types of question to be resolved Way evidence was produced Analytical approach 1. Type of Crime Evidence based on type of crime being analyzed: Homicide evidence
Burglary evidence Assault evidence Rape evidence Each case would have different types of evidence that would be found Example: no biological fluids in burglary case 2. Type of Material Evidence can be made up of different types of material
including Metallic evidence Glass evidence Paint evidence Plastic evidence Wood evidence Paper evidence 3. General Nature of Evidence Evidence can be classified as physical, chemical or biological
Physical firearm, tool Chemical drug sample Biological hair, bloodstains 4. Physical State of Evidence Evidence can be classified as solid, liquid or gas Solid most types of evidence such as clothing, glass, paper Liquid blood and accelerants
Gases very rarely collected includes gases and vapors at fire scenes 5. Type of Question to be Resolved Evidence is classified according to whether it will be used as an aid in reconstructing an event, linking a suspect to victim or to crime, excluding or exonerating a
victim 6. Way Evidence Was Produced Evidence is classified according to how it relates to the act under investigation Position movement or disturbance of objects Imprints and indentations Striations Tears/cuts
Transfer of matter 7.Laboratory/Analytical Approach Evidence is placed into categories according to whether it is simply to be identified, an individualization is sought or reconstruction of the event is desired Reconstruction wanted in cases involving gunshot residue
patterns, shotgun pellet patterns, blood stains or blood spatter patterns Common Types of Physical Evidence Blood Firearms Rubber Saliva
Glass Powder Docume Hair nts Drugs Explosiv es
Fibers Fingerpri nts Impressi residue Serial numbers Soil Tool marks Vehicle
Identification System (IAFIS) AFIS (individual) Combined DNA Index System (CODIS) National Integrated Ballistics Information Network (NIBIN) Integrated Ballistic Identification System (IBIS) Case Study Fort Collins, Colorado and
Philadelphia, Pennsylvania are separated by nearly 1800 miles but in 2001 they were tragically linked through DNA. Troy Graves left the Philadelphia area in 1999, joined the Air Force, and settled down with his wife in Colorado. Case Study A frenzied string of 8 sexual assaults
around the Colorado University campus set off a manhunt that ultimately resulted in the arrest of Graves However, his DNA profile inextricably identified him as Philadelphias notorious Center City Rapist This assailant attacked 4 women in 1997 and brutally murdered Shannon Schieber, a Wharton School graduate student in 1998 Case Study His
last known attack in Philadelphia was the rape of an 18 year old student in August 1999, shortly before he left the city In 2002 Graves was returned to Philadelphia where he was sentenced to life in prison without parole
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