Transcript Document
Firearms Identification The class characteristics obtained from an evidence bullet can narrow down the possibilities of the use of a certain type or make of weapon. However, the evidence bullet must be compared to a “test bullet” that has been fired from the suspect weapon in order to match individual characteristics. Firearms Identification In order to prevent damage to the test bullet’s markings and to facilitate the bullet’s recovery, test firings are normally made into a recovery box filled with cotton or into a water tank. The comparison microscope is used to compare the individual characteristics of the “evidence bullet” to those of the “test bullet”. Both bullets are viewed simultaneously within the same field of view. The examiner rotates one bullet until a well defined land or groove comes into view. The other bullet is rotated until a matching region is found. Firearms Identification Not only must the lands and grooves of the test and evidence bullet have identical widths, but the longitudinal striations on each must coincide. Firearm Identification The firearms examiner rarely encounters a situation in which a perfect match exists all around the bullet’s periphery. The presence of grit and rust can to some degree alter the markings on bullets fired through the same barrel. Firearm Identification As with fingerprint comparison, there are no hard and fast rules governing the minimum number of points required for a bullet comparison. The final opinion must be based upon the judgment, experience, and knowledge of an expert. Cartridge Casings All bullets have cartridge casings that may be analyzed for breechblock impression, firing pin impression, ejector marks, and extractor marks. Firing Pin Impressions and Breechblock Impressions Extractor Mark Shotguns Most shotguns have a smooth barrels. Therefore, projectiles passing through a shotgun barrel will not be impressed with characteristic markings. The diameter of a shotgun barrel is expressed by the term “gauge”. The higher the gauge, the smaller the barrel. Shotguns Gauge = the number of lead balls with the same diameter as the barrel that would make a pound. Exception – A .410-gauge shotgun has a barrel with a 0.410 inches in diameter. Shotguns Shotgun “shot” or “pellet” evidence can sometimes indicate the gauge of the shotgun. The shotgun shell can be analyzed in the same manner as a bullet cartridge casing. The “wad” typically flies approximately 10 – 15 feet from the shotgun barrel. If found, if can indicate the gauge of the shotgun used. Automated Firearm Search System DRUGFIRE The DRUGFIRE system was developed by the FBI and has been online since 1992. The image of the base of an expended cartridge is placed into the system. The breechblock marks and the firing pin impressions are the areas of interest for comparison. Automated Firearm Search System DRUGFIRE The DRUGFIRE system also incorporates a bullet imaging system which allows the examiner to image expended bullets into the system for comparison with other expended bullets. Automated Firearm Search System IBIS The IBIS system (Integrated Ballistics Identification System) is a technology that has been developed by the ATF (Bureau of Alcohol, Tobacco, and Firearms). It came online in 1991. Data storage system is similar to DRUGFIRE. Automated Firearm Search System NIBIN In 1999, the FBI and ATF signed a Memorandum of Understanding allowing the use of the National Integrated Ballistics Identification Network (NIBIN) to facilitate exchange of firearms data between DRUGFIRE and IBIS.