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Firearms investigators have long worked under a simple assumption: once a round is fired, any fingerprint left on the cartridge case is effectively destroyed. Heat, pressure, and friction inside the chamber tend to burn away the organic residues that conventional methods rely on, leaving analysts with little more than tool-mark traces to link evidence back to a weapon. A new technique developed at Maynooth University in Ireland suggests this limitation may not be permanent.
The research team has demonstrated an electrochemical process capable of revealing clear fingerprint patterns on spent brass casings within seconds. Instead of depending on sweat or skin oils, the method uses the fingerprint’s physical imprint as a protective mask. When a low voltage is applied, a thin metallic coating forms only on the exposed areas of the brass surface, leaving the ridge pattern untouched and creating a sharp, high-contrast negative image.
According to Interesting Engineering, this distinction is important because organic residues often evaporate or degrade during firing, while the physical deformation caused by a fingerprint can survive. Early trials show the technique works even on casings that have undergone significant thermal stress, offering investigators an opportunity to link ammunition not just to a firearm, but to a person — a connection previously considered unattainable after discharge.
For homeland security, law enforcement, and counterterrorism units, the ability to recover prints from fired casings could provide a new layer of intelligence in cases involving organized crime, firearms trafficking, or improvised weapons. Ammunition from shootings or attacks often appears without the firearm itself; any tool that strengthens the evidentiary chain can significantly improve investigative outcomes.
The researchers caution that the method is still under development. Surface corrosion, extreme heat exposure, and variations in metal type can all affect results. Stainless steel and aluminum remain more challenging than brass, and long environmental exposure reduces reliability. Before any courtroom use, the technique will require extensive validation, blind testing, and inter-laboratory replication.
Despite these limitations, the approach holds promise beyond ammunition. The same principles could apply to knives, explosive fragments, or other conductive materials exposed to heat. If broader testing confirms its reliability, this electrochemical process may become a valuable addition to the forensic toolkit — offering answers in cases where traditional methods fall short.
The research was published in the Forensic Chemistry Journal.
