Chapter_3_Physical_Evidence

Chapter_3_Physical_Evidence - 8/22/11 Locard's Exchange...

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8/22/11 1 Locard’s Exchange Principal: Whenever two objects come into contact with one another, there is an exchange of materials between them. What are we talking about? • Common Types • Identification and collection • Comparison –Individual vs. Class Characteristics • Crime-Scene Reconstruction
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8/22/11 2 Some Examples… Biological or natural origin – Blood, semen, saliva Found? fabric, cigarette butts, stains – Hair – both human and animal – Fingerprints – visible and latent – Organs and physiological fluids – detect drugs and poisons – Soil and minerals – embedded in shoes, material connected to crime – Wood and other vegetative matter – sawdust, shavings, packing material – Insect larvae 1 in 6 women and 1 in 33 men are sexual assaulted Insect Larvae
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8/22/11 3 Typical blowfly life cycle from egg deposition to adult fly emergence. This cycle is representative of any one of the nearly ninety species of blowflies in North America. Forensic Entomology The study of insects and their relation to a criminal investigation is known as forensic entomology. Forensic entymology commonly is used to estimate the time of death when the circumstances surrounding the crime are unknown. This determination can be carried out by studying the stage of development of maggots or insect sequence of arrival. After decomposition begins, insects that feed on the dead tissue infest the body and lay eggs, usually within 24 hours. The most common and important of these is the blowfly recognized by its green or blue coloration. Forensic entomologists can approximate how long a body has been left exposed by examining the stage of development of the fly larvae.
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8/22/11 4 Material of man-made origin – Drugs – bulk and trace levels – Explosives – chemicals and initiators – Fibers – natural and synthetic – Firearms- ammunition, gunshot residue – Glass – hit and run, break and enter – Paint – hit and run, transfer evidence – Petroleum Products – arson, lubricants – Plastics – linked to objects found on suspect – Documents – notes, records, obliterations Impression Evidence Impressions – Tool marks – crowbars, firing pins – Tear marks – tapes, plastic bags – Document impressions – writing – Tire prints, shoeprints
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8/22/11 5 Archaeology or CSI??? Process a crime scene vs examine a site for historical record of human activity – Snapshot of past activity – One way “careful dissection” – once an item is moved it will never exist in the same way. Must record the provenience (location) and context (relationship to other items) Important differences Safety – many of these scenes may be very hazardous – Inhalation hazards – smoke, solvents, gases, asbestos – Booby traps - bombs, electrical fixtures, light switches – Disease hazards - AIDS, hepatitis, TB, anthrax – Physical hazards – sharps, falling objects, spills – Presence of perpetrator
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Chapter_3_Physical_Evidence - 8/22/11 Locard's Exchange...

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