Created by C. Ippolito July 2007 Physical Evidence Objectives List the common types of physical evidence encountered at crime scenes. Explain the difference between the identification and comparison of physical evidence. Define individual and class characteristics. Give examples of physical evidence possessing these characteristics. Discuss the value of class evidence to a criminal investigation. List the number and types of computerized databases relating to physical evidence that are currently in existence. Explain the purpose physical evidence plays in reconstructing the events surrounding the commission of a crime. Updated 4/30/2019 Created by C. Ippolito July 2007
Common Types of Physical Evidence Blood, Semen, and Saliva on fabrics cigarette butts Documents handwriting typewriting paper, ink, obliterations charred/burned documents Drugs any illegal substances Updated 4/30/2019 Created by C. Ippolito July 2007
Common Types of Physical Evidence Explosives devices objects from scene Fibers natural synthetic Fingerprints hidden visible Updated 4/30/2019 Created by C. Ippolito July 2007
Common Types of Physical Evidence Firearms discharged ammo intact ammo Glass particles/fragments bullet holes in panes Hair animal human Updated 4/30/2019 Created by C. Ippolito July 2007
Common Types of Physical Evidence Impressions tires shoes bite marks Organs/Physiological Fluids evidence of drugs/poison alcohol levels Paint liquid/dry/chips cross transfers Updated 4/30/2019 Created by C. Ippolito July 2007
Common Types of Physical Evidence Petroleum Products arson accelerants grease stains Plastics bags used in crimes cross transfer Powder Residue GSR Serial Number restore ID firearms etc Updated 4/30/2019 Created by C. Ippolito July 2007
Common Types of Physical Evidence Soil/Minerals imbedded in shoes insulation on garments Tool Marks impressions Vehicle Lights Wood/Vegetative Matter wood, sawdust, pollen Updated 4/30/2019 Created by C. Ippolito July 2007
Examination of Physical Evidence Identification determine the physical or chemical identity of a substance adopt test procedure with characteristic results for standard materials test sufficient to exclude other substances Comparison subjects suspect specimen and a standard specimen to same tests to determine common origin select properties are chosen for comparison draw conclusion about origin Probability of likelihood of similar origin is important Updated 4/30/2019 Created by C. Ippolito July 2007
Individual Characteristics property possessed by evidence that can be associated with a common source with an extremely high degree of probability matching fingerprint ridge marks (1 x 1060) comparison of random striations on bullets or tools comparison of wear patterns in footwear or tires comparison of handwriting characteristics Updated 4/30/2019 Created by C. Ippolito July 2007
Class Characteristics evidence that can be associated with a group of specimens but cannot be singled out as coming from a single source single layer paint chip from a car blood types (26% of population has type A) need additional characteristics to “increase” probability of difference product rule overall probability of multiple characteristics existing together is the product of their individual probabilities Type A – 26%, EsD factor - 85%, PGM 2+2- - 2% total probabilit together .26 x .85 x .02 = .0044 or 1/200 Updated 4/30/2019 Created by C. Ippolito July 2007
Significance of Physical Evidence Forensic Science cannot for the most part assign exact or approximate probability values in the comparison of the vast majority of class physical evidence create databases of statistical significance Value of Class Physical Evidence does it corroborate events? variety of evidence convicted W. Williams in Georgia murders can more often can exonerate or exclude individuals When does evidence cross from “class” to “individual” how many ridges in a fingerprint? how many writing similarities? Updated 4/30/2019 Created by C. Ippolito July 2007
Natural vs Evidential Variation Modern analysis can find differences in the same material Criminalists must distinguish natural variation from evidential variation at one magnification paint chips indistinguishable at greater magnification difference can be discerned when are the differences and similarities significant? Updated 4/30/2019 Created by C. Ippolito July 2007
Created by C. Ippolito July 2007 Forensic Databases Integrated Automated Fingerprint Identification System (IAFIS) FBI maintained fingerprints and criminal histories of 50 million individuals scanned latent can be compared by computer and list of possible matches will be returned similar systems in other countries Combined DNA Index System (CODIS) DNA profiles Forensic Index – 110,000 profiles of unknowns from unsolved crimes Offender Index – 3 million profiles of convicted/arrested individuals National Integrated Ballistics Information Network (NIBIN) Bureau of Alcohol Tobacco Firearms and Explosives maintained ballistic images stored and correlated submitted by local jurisdictions International Forensic Automotive Paint Data Query (PDQ) RCMP maintained chemical and color information on original automotive paints Shoeprint Image Capture and Retrieval (SICAR) commercially maintained database for shoe sole patterns (8,000) form 300 shoe manufacturers Updated 4/30/2019 Created by C. Ippolito July 2007
Crime Scene Reconstruction examining evidence to reconstruct the events that occurred before, during, and after the commission of a crime evidence supports a likely sequence of events collaboration and collect /analysis of data by: medical examiners criminalists law enforcement Updated 4/30/2019 Created by C. Ippolito July 2007