Evidence processing (Forensic Science)
After a crime scene has been secured and thoroughly documented, the next step is to process the evidence. The primary steps in evidence processing are identification, evaluation, and collection of evidence. These procedures are most often the responsibility of crime scene technicians or specialists. Depending on the type of crime scene, specialists may be enlisted to collect particular types of evidence. For example, arson investigators may be brought in to process the evidence at scenes of suspected arson or at scenes where explosives are found.
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Evidence Identification and Collection (Forensic Science)
The types of evidence identified and the techniques utilized to collect the evidence fully depend on the nature of the crime. For example, the evidence processing at a crime scene involving a homicide is quite different from that conducted at a crime scene involving a burglary or a drug bust. At a typical crime scene, evidence is initially identified during the search process. This very methodical process can take different forms; for example, a crime scene may be searched in a spiral, grid, parallel, or zone pattern. The objective of all crime scene search patterns is the same, however: to facilitate the identification and collection of evidence that may be helpful to investigators while minimizing the likelihood that searchers will contaminate any evidence.
After evidence is identified, it must be prioritized for collection, and the collection process must be thorough and methodical. Crime scene technicians have one chance to get it right—if evidence is overlooked, the strength of the criminal case may be significantly affected. Fragile evidence takes priority and is often collected as quickly as possible. Such evidence may include perishable evidence, fingerprint evidence, or evidence that may be easily lost. The typical types of evidence collected at crime scenes include but are not limited to trace evidence (such as gunshot residue), body fluids (such as blood), impressions (including...
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Packaging and Labeling (Forensic Science)
The final steps of evidence processing entail the packaging and labeling of evidence samples in preparation for their transport to the crime laboratory for analysis. It is important that crime scene technicians follow established guidelines in packaging evidence so that the samples are properly preserved. Most often, evidence samples are placed individually into various sizes and types of paper bags. Individual items must be kept separate to prevent cross-contamination. Plastic bags and other plastic containers are avoided because they facilitate the deterioration of evidence. Not all types of evidence are packaged in paper bags, however; for example, unstable liquids, such as gasoline, are typically collected in glass jars.
The general process for packaging and preserving biological evidence samples involves allowing each sample to air-dry, packaging it in a paper bag, and then refrigerating or freezing it. For example, a bloodstained shirt would be allowed to dry completely before it is packaged in a paper bag, refrigerated or frozen, and transported to the crime laboratory. When this is not possible, the evidence must be packaged at the crime scene and quickly transported to the crime laboratory, where it is then completely dried and properly packaged. In situations like this, a time limit (often a matter of hours) is usually placed on how long the evidence can be packaged while wet before it is considered useless...
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Further Reading (Forensic Science)
Bennett, Wayne W., and Kären M. Hess. Criminal Investigation. 8th ed. Belmont, Calif.: Wadsworth/Thomson Learning, 2007. Provides comprehensive discussion of the procedures and techniques used by investigators at crime scenes.
Fisher, Barry A. J. Techniques of Crime Scene Investigation. 7th ed. Boca Raton, Fla.: CRC Press, 2004. Presents detailed information on the methods used in the collection and preservation of evidence found at crime scenes.
Gardner, Ross M. Practical Crime Scene Processing and Investigation. Boca Raton, Fla.: CRC Press, 2005. Describes the practical application of methods and procedures of crime scene processing.
Lyman, Michael D. Criminal Investigation: The Art and the Science. 5th ed. Upper Saddle River, N.J.: Pearson Prentice Hall, 2008. Textbook discusses the fundamentals of crime scene investigation and relevant technological advances. Also explores the roles and responsibilities of police officers and criminal investigators.
National Institute of Justice. Crime Scene Investigation: A Guide for Law Enforcement. Washington, D.C.: U.S. Department of Justice, 2000. Report intended for law-enforcement administrators and trainers of crime scene investigators addresses the general procedures and methods to be followed at crime scenes, including initial response, documentation, and the evaluation and processing of evidence.
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