Identification Techniques Used for Firearms, Tool Marks, and Other Impressions

1044 Words Mar 2nd, 2016 5 Pages
Since the early 20th century, the practice of firearm and toolmark identification or comparison has been a crucial factor in forensic science. Agencies such as the FBI have introduced a standard operating procedure which helps to identify weapons and toolmarks. There are certain criteria that must be met to be considered a match. These criteria include multi-level matching of the items brought from the scene of a crime with the test specimens. (http://www.fbi.gov/about-us/lab/forensic-science-communications/fsc/july2009/review/2009_07_review01.htm).
“The examination process typically begins when an examiner receives a suspect firearm, along with bullets (the projectiles) and spent cartridge cases recovered from a crime scene.”
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Bullets are soft and somewhat malleable as they are typically made of lead. As a bullet twists upon firing, the striations will be determined by the direction in which the bullet spins. If the impressions on the bullet vary, then it is safe to say it could not have been fired from the same weapon (Saferstein, p. 209).
The inner workings of a firearm which are responsible for creating impressions on a bullet are as follows: the firing chamber, breech face, firing pin, ejector, extractor and the rifling of the barrel. Characteristics transferred to the cartridge case include: firing pin impression, center of firing pin impression, and ring of firing pin impression. In a study by Md Ghani et al in 2010, 96.7% of the time these features were able to connect the cartridge case to the firearm. (http://library.med.utah.edu/WebPath/TUTORIAL/GUNS/GUNLAB.html).
Tool marks, which are any “impression, cut, gouge, or abrasion caused by a tool coming into contact with another object” (Saferstein, p. 232) are frequently found at crime scenes involving burglary or other forced entry into a building or safe. Typically, tool marks can be made via the use of screwdrivers, knives, or crowbars. The result is an indentation left by the prying action of such implements. Because tools are manufactured with microscopic irregularities, they leave these markings on whatever soft surface they are pushed upon. Simple use of a comparison microscope can determine what appear to be

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