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what are some key steps in securing and identifying both physical and biological evidence at a crime scene?
A successful crime investigation depends upon the collection and analysis of various kinds of evidence. Forensic scientists classify evidence in different ways and have specific ways of dealing with it. [ One major distinction is between physical and biological evidence. Physical evidence refers to any item that comes from a nonliving origin, while biological evidence always originates from a
living being. The most important kinds of physical evidence are fingerprints, tire marks, footprints, fibers, paint, and building materials. Biological evidence includes bloodstains and DNA. Locard's Exchange Principle dictates that evidence, both physical and biological, is to be found at the scene of a crime because the perpetrator always leaves something behind by having contact with victims and objects there. Similarly, he or she will often take something away with them, which can be found on a search of their person, their garment, a vehicle, or their premises. Such evidence is often found in minute quantities and known as trace evidence. One important source of physical trace evidence is textile fibers, which usually comes from clothing or furniture involved in the crime. It may either be left behind by the perpetrator or picked up from the victim. Typically, trace evidence is invisible to the naked eye and is collected by brushing or vacuuming a suspect surface. Once collected and back in the laboratory, microscopic techniques will often be used in its examination and analysis as, for example, in the case of paint fragments or textile fibers. ]
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Asked 10/30/2012 2:24:15 AM
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how an arson investigation must be handled. explain in detail some of the challenges that could be encountered in detail.
Weegy: Fire investigation involves the examination of all fire-related incidents once firefighters have extinguished the fire. [ The practice is similar to the examination of crime scenes in that the scene must be preserved and evidence collected and analysed, but with numerous additional difficulties and dangers. The investigation will include closely surveying the damaged scene to establish the origin of the fire and eventually establishing the cause. However in order to effectively examine and evaluate a fire scene, it is imperative that the investigator has a detailed knowledge of the chemistry and behaviour of fire and its effects. Nature & Chemistry of Fire Fire occurs due to the exothermic reaction of combustion (burning), producing heat and light. In order for a fire to occur, three vital components must be present: a fuel source, an oxidant (often O2) and a sufficient amount of energy in the form of heat. Together these make up the fire triangle. More recently a fourth factor has been described – a self-sustaining chemical chain reaction – to produce the fire tetrahedron. The absence of any of these conditions will result in a fire not starting or extinguishing through smothering (oxygen removal), cooling (heat removal) or starving (fuel removal). Solid and liquid materials do not actually combust, but the process of heating causes them to produce vapours which can burn. This is the process of pyrolysis. Through this pyrolysis products will be formed, flammable and volatile substances of low molecular weight caused through the decomposition of materials by fire. The colour of flames can vary depending on the materials involved in the combustion. The colour of a flame is basically determined by the wavelength of light emitted, which varies depending on the material. For example, red/yellow/orange flames are commonly encountered when carbon is present. Inorganic substances can produce more obvious colour differences, such as copper which will cause ... (More)
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