Summary of the Examination Method
The examination methodology is a process that begins with the evaluation of the class characteristics and ends with the analysis of individual characteristics. This process is outlined below.
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). 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 (1). 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 (2).
A verification process is employed to ensure proper conclusions are rendered. As outlined in a laboratory's quality assurance policy, a mechanism should be in place to determine which cases will require verification (3).
- Association of Firearms and Tool Mark Examiners (AFTE) "Theory of Identification" AFTE Journal (July 1992 Volume 24, Number 3)
- Association of Firearms and Tool Mark Examiners (AFTE) "Theory of Identification" AFTE Journal (Fall 2011 Volume 43, Number 4)
- Elimination Factors Related to FA/TM Identification, SWGGUN
- SWGGUN Quality Assurance Guidelines, SWGGUN
- Association of Firearms and Tool Mark Examiners (AFTE) Procedures Manual FA-IV-13