Masters Thesis

Individuality of toolmark impressions using firing pins for a .45 caliber Glock pistol

The science underlying firearm and toolmark identification is thoroughly documented and has been accepted by scientists around the world for over a century. However, in a day and age where instruments are fully automated and population genetics allow a suspect_s DNA to be discriminated to the billions, the traditional approach to toolmark identification seems archaic. A more objective means of identifying a toolmark, other than basing a conclusion on an examiner_s training and experience may be warranted. Several new examination methods have been discussed, such as computer algorithms and three-dimensional imaging. These methods tend to require specialized training and are not cost effective for forensic laboratories. More immediate solutions, such as standardization and statistical models, are much more practical to the forensic science community. Impressed evidence is often overshadowed by striated toolmarks, although it often holds equally valuable information for toolmark examiners due to the particular way in which a tool is manufactured or the wear and abuse imparted on the tool. This study evaluates impressed markings from firing pins to establish their value to examiners. Attempts will be made to objectify identification by characterizing individual features within an impression using a hypothetical classification system, followed by quantification using probability estimates. Firing pin impressions are frequently found to contain unique characteristics that reproduce well on test fired cartridge cases. However, there is high variability among cartridge cases of different manufacture, which could be due to the metallurgic properties of cartridge cases.

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