Amicus Brief in Support of Excluding Firearm and Toolmark (FA/TM) Identification Evidence

This brief explains why expert testimony on firearm and toolmark (FA/TM) identification should be excluded. FA/TM identification is premised on the unproven assumption that each firearm leaves unique, accidental, and individualized markings on spent ammunition despite evidence from several studies that this analysis lacks sound estimates of error rates, is characterized as subjective pathological science, and is not based on reliable scientific principles. This brief collects empirical studies and evidence demonstrating that FA/TM identification lacks scientific validity (pp. 14-22), and it explains the methodological problems and high error rates associated with various studies used to attempt to validate FA/TM identification (pp. 22-43). Because of the imprecise and problematic nature of FA/TM identification, the brief also contends that experts should not be allowed to testify about characteristics of spent ammunition that imply a match (pp. 49-59).