Here’s what you’ll learn when you read this story:

• Since the dawn of modern fingerprinting, lifting prints from bullet casings has been thought to be impossible due to damage caused by the intense temperatures, gas, and friction of firing a gun.
• A new study uses an electrochemical process that essentially turns the brass casing into a kind of electrode that draws chemicals toward the surface and then fills in gaps between hidden ridges, revealing a fingerprint.
• Additional work will need to be done to both ensure the technique’s accuracy and develop the means to use this method on other hard-to-fingerprint surfaces.

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In October of 1904, the St. Louis Metropolitan Police Department became the first in the nation to create a fingerprint bureau (inspired in part by the policing challenges of the 1904 World’s Fair). And in the ensuing 120 years, not only has the crime-fighting technique spread far and wide, but it has improved in both reliability and accuracy, and is now even incorporating artificial intelligence in an attempt to learn more about human fingerprints themselves.

However, all of that time, scientists haven’t cracked arguably the most important problem facing fingerprinting: You can’t pull prints off of bullet casings. Because of the intense temperatures, gas, and friction applied to a bullet when fired, biological residue (read: fingerprints) typically doesn’t survive the process. If crime scene investigators could somehow lift prints off these littered casings... well, that’d be quite the smoking gun.

A new study led by scientists at Maynooth University in Ireland might be making impressive headway on that very idea. As reported in the journal Forensic Chemistry, authors Colm McKeever and Eithne Dempsey wrote that a new electrochemical technique can draw chemicals to the surface of the casing when a low voltage is applied, filling tiny gaps between fingerprint ridges 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 visualization,” McKeever said in a press statement. “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 tested this next-gen fingerprinting technique on brass, as it’s the most widely used material for bullet casings (certain aluminum alloys and even steel are used in some cases), and found that this electrochemical process even worked on samples as old as 16 months. But the best part may be that at the heart of this technology is a device known as a potentiostat (which is what controls the voltage), and it can be as small as a mobile phone, meaning that future kits could be compact enough to carry into the field.

“With this method, we have turned the ammunition casing into an electrode, allowing us to drive chemical reactions at the surface of the casing,” McKeever said in a press statement.

The authors note that this study is only a proof-of-principle first phase in visualizing fingerprints on challenging surfaces. Further work will need to be done to shore up the technique’s accuracy before it’s exported around the world as a crime-fighting tool (time well spent, considering conventional fingerprinting doesn’t exactly have a sterling success record). The team hopes that this process could also be applied to other metallic surfaces, including knives, coins, and other types of firearms.

For more than a century, bullet casings have only informed law enforcement about the gun used in a crime. But this new research presents a major possibility that, someday soon, they could provide much more than that.

Darren lives in Portland, has a cat, and writes/edits about sci-fi and how our world works. You can find his previous stuff at Gizmodo and Paste if you look hard enough.