Gunshot residue and brakepads: Compositional and morphological considerations for forensic casework

Area of Science:

• Forensic Science
• Materials Science
• Automotive Engineering

Background:

• Previous studies suggested automotive brake pads could mimic gunshot residue (GSR).
• These findings emerged when lead was being phased out of automotive components.
• The relevance of brake pads as a source of GSR-like particles in contemporary vehicles remains uncertain.

Purpose of the Study:

• To investigate if modern automotive brake pads produce particles compositionally and morphologically similar to GSR.
• To assess the prevalence of lead, barium, and antimony in particles from current brake pads.
• To differentiate brake wear particles from actual firearm discharge residues.

Main Methods:

• Collected 75 brake pads from contemporary vehicles in Adelaide, South Australia.
• Screened pads using X-ray fluorescence (XRF) and selected 12 representative samples.
• Analyzed particle composition using scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) and an automated GSR search.

Main Results:

• No three-component particles (lead, barium, antimony) were detected on brake pads or associated surfaces.
• Particles containing barium and antimony were common, often angular and containing sulfur.
• These brake particles were frequently found alongside abundant iron-containing particles, aiding differentiation from firearm residues.

Conclusions:

• The likelihood of modern brake pads generating three-component 'GSR-like' particles is significantly lower than previously reported.
• Barium and antimony particles from brakes can be distinguished from GSR based on morphology, elemental composition (presence of sulfur), and association with iron particles.
• Current brake pad formulations and wear debris are unlikely to be confused with gunshot residue in forensic analyses.