How Probative is Comparative Bullet Lead Analysis?

Abstract

For more than 35 years, forensic expert witnesses have testified that they can associate bullets recovered from the scene of a crime to bullets in the possession of a suspect "to a reasonable degree of certainty" based on analyses of the compositional constituents of the lead. This paper refutes the scientific foundation and probative value of claimed "matches." The underlying premises of comparative bullet lead analysis (CBLA) contravene well-established metallurgical principles and phenomena known to exist in smelting practice. Comprehensive literature review reveals no meaningful or comprehensive study or data establishing the assumptions that forensic samples (10-70 mg.) are compositionally representative of their molten source, that molten sources are unique in composition, or that retail distribution after manufacture is homogeneous (precluding regional concentrations of analytically indistinguishable product). The premises underlying the forensic practice, metallurgical considerations during the manufacture (smelting) of bullet lead, and legal implications of product distribution to probative value are discussed.

Keywords: forensic, bullet lead, comparative bullet lead analysis, CBLA