Comparative Bullet Lead Analysis: A Case Study in Flawed Forensics

Abstract

Expert testimony about compositional bullet lead comparisons, known as comparative bullet lead analysis (CBLA), has been admitted in criminal trials without comprehensive or meaningful validation studies, and without significant challenge, for close to 40 years. The underlying premise and ultimate inference of "same composition = same source" has been intuited for virtually the entire history of forensic application. Recent metallurgical studies have revealed serious flaws in the underlying theory and assumptions, forensic practice, and conclusions of bullet lead experts. Numerous vulnerabilities and criticisms in the 2004 Report of the National Research Council of the National Academy of Sciences (NAS) are presented and discussed. The author and the NAS both conclude that available data do not support any statement that a crime scene bullet originated from a particular box or boxes of ammunition, or to a particular molten source at a manufacturer.

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