Scientists achieve forensics’ “Holy Grail” by recovering fingerprints from fired bullets

Dr. Eithne Dempsey and her former PhD student, Dr. Colm McKeever, from the Department of Chemistry at Maynooth University in Ireland, have designed a novel electrochemical process that reveals fingerprints on brass casings even after exposure to the intense heat generated when a gun is fired.

Solving a Long-Standing Forensic Challenge

For decades, forensic experts have struggled to retrieve fingerprints from firearms or ammunition. The extreme temperatures, gas, and friction produced during gunfire typically destroy any biological residue. Because of this, many criminals have relied on the assumption that fired weapons and casings could not link them to a crime scene.

"The Holy Grail in forensic investigation has always been retrieving prints from fired ammunition casings," said Dr. Dempsey. "Traditionally, the intense heat of firing destroys any biological residue. However, our technique has been able to reveal fingerprint ridges that would otherwise remain imperceptible."

The research team discovered that coating brass casings with a thin layer of specially chosen materials can expose hidden fingerprint ridges. Unlike many existing forensic methods, this approach does not rely on toxic chemicals or expensive, high-powered equipment. Instead, it uses environmentally friendly polymers and requires very little energy to produce clear fingerprint images in seconds.

The process works by placing a brass casing inside an electrochemical cell filled with a chemical solution. When a low electrical voltage is applied, the chemicals are drawn toward the surface, filling the tiny gaps between fingerprint ridges and forming a distinct, high-contrast image. The result appears almost instantly.

"Using the burnt material that remains on the surface of the casing as a stencil, we can deposit specific materials in between the gaps, allowing for the visualisation," said Dr. McKeever.

Durable Results and New Investigative Possibilities

Tests showed that this technique also worked on samples aged up to 16 months, demonstrating remarkable durability.

The research has significant implications for criminal investigations, where the current assumption is that firing a gun eliminates fingerprint residues on casings.

"Currently, the best case of forensic analysis of ammunition casings is to match it to the gun that fired it," said Dr. McKeever. "But we hope a method like this could match it back to the actual person who loaded the gun."

The team focused specifically on brass ammunition casings, a substance that has been traditionally resistant to fingerprint detection and is the most common type of material used globally.

The researchers believe that the test for fingerprints on brass they have developed could be adapted for other metallic surfaces, expanding its range of potential forensic applications, from firearm-related crimes to arson.

This technique uses a device called a potentiostat, which controls voltage and can be as portable as a mobile phone, making it possible to create a compact forensic testing kit.

"With this method, we have turned the ammunition casing into an electrode, allowing us to drive chemical reactions at the surface of the casing," said Dr. McKeever.

Toward Real-World Use

Although early results are promising, the new fingerprint recovery method will need further testing and validation before it can be used by law enforcement agencies around the world. The project, supported by Research Ireland and Maynooth University, was recently published in a leading forensic science journal and represents a major step forward for global policing and criminal investigation.