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 committing a crime
Physical Evidence Linking a suspect with a victim – Locard’s 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 Witness’s Testimony – analysis can indicate whether a person’s 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 Locard’s 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 substance’s 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 victim’s clothing may match paint taken from a suspect’s 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
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 tshirt. 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 spatterns
Common Types of Physical Evidence �Blood �Glass �Powder residue �Documents �Impression �Serial numbers s �Drugs �Explosives �Organs/ph �Soil ys fluid �Tool marks �Fibers �Vehicle �Fingerprint �Paint �Plastic bag lights s �Rubber �Firearms �Saliva �Hair
Forensic Databases �Integrated Automated Fingerprint 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 Philadelphia’s 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