Determining the specific gun that fired a bullet is a complex process known as ballistic fingerprinting or forensic firearm examination. While it is not always possible to definitively identify the exact gun, firearms examiners use various techniques and tools to analyze bullet casings and compare them to test-fired bullets from suspected firearms. Here are the general steps involved:
Visual Examination: The bullet casing is visually inspected for marks, such as firing pin impressions, extractor and ejector marks, and other distinctive features left by the firearm during the firing process.
Microscopic Analysis: A comparison microscope is used to examine the marks on the test-fired bullet from a suspect firearm and the recovered bullet. The examiner looks for similarities in striations (fine lines and grooves) caused by the barrel and the unique characteristics of the firearm's rifling pattern.
Bullet and Casing Comparison: Both the recovered bullet and the test-fired bullet are compared in terms of class and individual characteristics. Class characteristics include the caliber, bullet type, and general rifling characteristics. Individual characteristics are unique marks, imperfections, or wear patterns that may be present on the bullet or casing.
Toolmark Examination: Firearms examiners use specialized tools such as comparison microscopes, magnifiers, and computer-based imaging systems to examine toolmarks left on the bullet and casing. These toolmarks are created by specific components of the firearm, like the firing pin, extractor, and ejector, which leave distinct patterns.
Database Comparison: If a potential suspect firearm is identified, examiners may compare the recovered bullet or casing to a database of known firearms and their test-fired bullets or casings. This comparison can help determine if there is a match or similarity to a specific firearm in the database.
It's important to note that the ability to identify a specific firearm depends on the condition of the recovered bullet and casing, the quality of the firearm examination process, and the availability of a reliable database for comparison. In some cases, a positive identification may be inconclusive or not possible due to the limitations of the evidence.