Role of a Firearm and Toolmark Examiner
The role of a Firearm and Toolmark Examiner is to formulate opinions relative to submitted firearm and tool evidence which otherwise stands mute. Fully qualified Examiners, based on their training, research, and acquired knowledge, stand prepared to give voice to this otherwise mute evidence.
The St Louis County Police Crime Laboratory currently has four such full-time Firearm and Toolmark Examiners. In addition to simple firearm safety and function checks, it is the responsibility of these Examiners to evaluate and compare submitted evidence related to tools of any kind with the impressions they are suspected to have made. (Keep in mind that firearms are actually a specialized tool making impressions on other components, i.e. bullets and cartridge cases.)
This examination process includes the following phases:
The initial examination phase evaluates evidence to determine if the observed class characteristics are the same between two specimens (two unknown specimens, or an unknown and a known specimen). If the specimens are suitable for examination and the class characteristics are the same, then it is possible that the toolmarks were produced utilizing the same tool (such as a firearm or a bolt cutter). If they are different, then the two specimens can be eliminated as being produced by the same tool.
If the class characteristics are consistent between two specimens, then a comparative examination is performed utilizing a comparison microscope. The methodology utilized in the examination process is pattern matching. This comparison is conducted to determine: 1) if any marks present are subclass characteristics and/or individual characteristics, and 2) the level of correspondence of any individual characteristics.
If sufficient agreement of individual characteristics is observed between two specimens, an identification conclusion is rendered. If all of the discernible class characteristics are the same, but sufficient agreement of the individual characteristics is not observed, then an inconclusive (no-conclusion) determination is rendered. In exceptional situations, an elimination conclusion may be rendered on observed differences in individual characteristics.
A verification process is employed to ensure proper conclusions are rendered. As outlined in our laboratory’s quality assurance policy, a mechanism is in place to determine which cases require verification.
Another duty of our Examiners is to restore obliterated serial numbers on firearms or other items. After preparing the surface, the Examiner applies different chemical solutions to restore the numbers. After a case is worked, an Examiner will write a detailed report concerning scientific findings related to Firearm and Toolmark analysis. Then, upon request, the Examiner will testify in criminal proceedings based upon these findings as an expert witness in the area of Forensic Firearm and Toolmark examinations.
The National Integrated Ballistic Information Network (NIBIN)/ Integrated Ballistics Identification System (IBIS) is a national database of digital images of ballistic evidence found at crime scenes or test-fired from confiscated weapons. The Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF) manages the system.
Examiners have access to the national database to capture and compare ballistic evidence to aid in solving and preventing violent crimes involving firearms. Specimens entered into NIBIN/IBIS are scored then searched and correlated with similarly scored specimens previously entered by our laboratory and other agencies. Automated searches are regional (entries from the St. Louis Metropolitan Area, Missouri State Highway Patrol and Illinois State Police – Belleville Laboratory), but manual searches of any participating agency in the world are possible. Although each specimen is actively searched only once, it is forever retained in the database and searched with each new submission of the same caliber. Our Examiners have discovered hundreds of case relationships using NIBIN/IBIS