Sponsored by DNA Labs International
Firearms turn up in countless criminal investigations; sometimes as the center of violence, sometimes as the only piece of physical evidence left behind. Often, they hold stories waiting to be told in the faintest hints of human biology: skin cells, sweat, trace DNA. But turning those microscopic traces into court-ready evidence is happening every day in laboratories around the world.
Not so long ago, many cases involving guns hit dead ends. Not for lack of effort, but because the science wasn’t quite able to pull through. DNA on a trigger guard or grip, exposed to heat, handled by many, cleaned or wiped were some of the many obstacles that erase or degrade what little biological material remains. In one case of ours, a firearm used in a robbery yielded nearly nothing from the initial swabs. It was only after swabbing the firearm a second time and using more sensitive extraction methods that analysts began to see results. Careful interpretation with probabilistic software then revealed a partial DNA profile which was enough to help guide investigators toward new leads.
These stories are no longer rare exceptions. Across crime laboratories and research centers, techniques have matured, and tools have improved. With new additions to the DNA toolbox, like SPENTSHELL™ technology for fired cartridge cases, the path from crime scene to courtroom is becoming more navigable.
The Challenges: Where Most Evidence Stalls
Every crime scene presents its own trials. When DNA is sought from firearms:
- The biological material is often low or badly degraded. Heat, exposure, cleaning, and environmental elements all conspire to destroy or disperse what little DNA there is.
- Firearms and spent casings are typically made of metal, often with finishes or coatings that either prevent adhesion or introduce chemicals that interfere with downstream DNA processes.
- Multiple handlers from victims, suspects, officers, crime lab personnel mean that contamination and mixed DNA profiles are more than common. Distinguishing primary DNA from secondary transfer, or parsing mixtures, pushes technical and legal boundaries.
- Inconsistent procedures from crime scene personnel across thousands of jurisdictions in the United States means inconsistent collection techniques.
- Time matters. The longer the delay in evidence collection or in transporting items under uncontrolled conditions, the more likely DNA degrades or is lost.
These challenges are why many laboratories, even when they succeed in extracting DNA, often end up with partial profiles or complex DNA mixtures deemed inconclusive.
What’s Working: How Science Is Moving the Needle
Despite the arduous obstacles ahead, there are reasons for optimism. Leading practitioners are refining strategies that raise the odds of usable DNA, even from tough substrates like guns and casings.
One key method is more thoughtful collection. Instead of a single dry swab, many crime scene teams now use a wet swab followed by a dry one (double-swabbing) or deploy specialized swabbing methods using more sensitive swabs than the typical cotton swab and advanced wetting solutions, like SPENTSHELL™. Training to target likely contact zones, such as the grip, trigger guard, areas handled directly, also vastly improves yield.
Laboratories are adapting their extraction and amplification protocols to the realities of trace and degraded samples. This means more sensitive kits for low-template DNA, stringent inhibitor removal when dealing with powdered residue or metal surface chemicals, concentration steps, and rigorous validation.
Then there’s mixture interpretation. When DNA from multiple individuals is present (either from successive handling or contamination), newer probabilistic genotyping tools, like STRmix™ software, allow analysts to model statistical likelihoods rather than simply rejecting the sample. This allows the scientist to analyze DNA profiles that would have previously been categorized as inconclusive.
From Forensic Science to Courtroom Story
All of these technical improvements are essential, but they mean little unless they survive legal scrutiny. Collectors must understand best handling practices and document every step: who handled the item, when, how; ensure chain of custody; minimize contamination; preserve evidence properly. Analysts must be able to explain their methods, limitations, and statistical strength. Prosecutors must understand the science in addition to the law: how courts view trace DNA, transfer issues, admissibility standards, expert testimony.
In one memorable trial, the prosecution’s expert walked through evidence from a firearm that had been collected rapidly after seizure, handled under strict protocols, and processed with low-copy DNA methods. At trial, defense raised questions of contamination and mixture. Because the lab’s procedures were well-validated, documentation thorough, and the expert clearly explained the possibility of mixed profiles and the weight (and limits) of the DNA comparison, the evidence was admitted and provided additional information to the jury.
What’s Possible When Science, Practice, and Law Align
We stand today at a promising crossroad. The collection tools are more sensitive. Lab protocols more powerful. Legal frameworks more adapted to trace and partial DNA. But consistency is still the challenge. Not every jurisdiction has access to the newer technologies. Not every crime lab has well-validated collection methods or mixture protocols. And not every prosecutor’s office is familiar with how to present trace DNA evidence, so it withstands scrutiny.
That’s why shared training, cross-disciplinary workshops, and case studies are so important. Out in the field and in the courtroom, we’re seeing what works, what doesn’t, and how small improvements in technique or documentation can make the difference between evidence that’s dismissed and evidence that changes lives.
An Invitation to Deepen Practice
If you are going to be at the upcoming ISHI conference, there is an opportunity to step deeper into these techniques. The Thursday afternoon DNA & Firearms Workshop will bring voices from each part of the chain, from collection to courtroom, to share both breakthroughs and real-world hard lessons. We’ll cover crime scene strategies, lab methods (including trace DNA, spent casings, unique firearms), mixture interpretation, and what prosecutors need for testimony and admissibility.
The science is moving fast. The opportunity to apply it with rigor and clarity is here. If you’re ready to sharpen your practice and improve outcomes, this workshop is meant for you.