Forensic test recovers fingerprints from fired ammunition casings despite intense heat.

A pioneering new test that can recover fingerprints from ammunition casing, once thought nearly impossible, has been developed by two Irish scientists. For decades, investigators have struggled to recover fingerprints from weapons because any biological trace is usually destroyed by the high temperatures, friction and gas released after a gun is fired. As a result, criminals often abandon their weapons or casings at crime scenes, confident that they leave no fingerprint evidence behind.

Dr. Eithne Dempsey, and her recent Ph.D. student Dr. Colm McKeever, of the Department of Chemistry in Ireland’s Maynooth University have developed a unique electrochemical method which can visualise fingerprints on brass casings, even after they have been exposed to the high temperature conditions experienced during gunfire.

“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”.

Latent finger-marks arise from natural secretions of the skin (produced by eccrine and sebaceous glands) remaining on a surface following contact. Eccrine sweat is ca. 98 % water, containing inorganic (chlorides, ammonias, phosphates) and organic (amino acids, urea, sugars) species, while residue from sebaceous glands contains mostly organic compounds (glycerides, fatty acids, sterol esters).

There are a wide variety of visualisation techniques for finger-mark evidence at the disposal of forensic professionals and choice of approach relies on the type of surface (porous/non-porous), the material on which the mark has been deposited, i.e., metallic, plastic, magnetic, glass, paper and the quality of the finger-mark & its age, environmental degradation, smudging.

Common visualisation methods can be categorised as powder or chemical visualisation. Chemical and biological evidence may be destroyed in the case of fired ammunition relevant to forensic ballistics, spurring an interest in alternative enhancement methods for challenging samples.

The team found they could coat brass casings with a thin layer of specialised materials to make hidden fingerprint ridges visible. Unlike existing methods that need dangerous chemicals or high-powered equipment, the new process uses readily available non-toxic polymers and minimal amounts of energy to quickly reveal prints from seemingly blank surfaces.

It works by placing the brass casing of interest in an electrochemical cell containing specific chemical substances. When a small voltage is applied, chemicals in the solution are attracted to the surface, coating the spaces between fingerprint ridges and creating a clear, high contrast image of the print. The fingerprint appears within seconds as if by magic! “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.

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. 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. While promising, the new technology faces rigorous testing and validation before it could potentially be adopted by law enforcement agencies worldwide.

Team Maverick