A firearm discharged with lead-free, heavy-metal-free primers is seized in a homicide investigation. SEM-EDX of adhesive lifts from the shooter's hands shows no lead-barium-antimony particles. What is the correct interpretation?

• A The suspect definitely did not fire a weapon
• B Absence of the classic triad excludes firing only if barium alone is also absent
• C The result confirms firing, because all primers produce the classic triad
• D Firing cannot be excluded, since such primers deposit particles containing elements such as strontium, titanium, zinc or gallium instead ✓

Explanation

Modern lead-free primers replace lead styphnate, barium nitrate and antimony sulphide with alternatives such as diazodinitrophenol initiators and strontium, titanium, zinc or gallium compounds, so the classic Pb-Ba-Sb particle never forms. A negative triad result therefore cannot exclude firing with such ammunition. Option C is wrong because the triad is not universal, and option A wrongly treats a screening-type negative result as proof of non-participation.

Reference: Knight's Forensic Pathology, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.