Matthew Gault · Jul 16, 2025
Early studies show that 3D printers may leave behind similar toolmarks on repeated prints.
So-called 3D-printed ghost guns are untraceable firearms that can be assembled at home. But cutting edge work from a forensic expert in California and researchers at the University of Oklahoma may soon show investigators can trace a 3D printed object to the specific printer that made it.
Weapons manufactured using 3D printers have been a subject of Biden-era legislation and recent Supreme Court scrutiny. It’s possible to download the blueprints for a firearm and build it in your home. There’s no serial number to track and no store to scrutinize your purchase. Luigi Mangione used a ghost gun to allegedly assassinate United Healthcare CEO Brian Thompson.
Kirk Garrison, a forensics expert who works for the San Bernardino Sheriff’s department, told 404 Media he’s had early success matching 3D printed objects to the machines that made them. Garrison said his comments represent his own views and not those of the San Bernardino Sheriff’s department. He also cautioned that what he’s doing is in its infancy and it might be years before authorities can reliably match a gun to the machine that made it, if they can do it at all.
In 2018, Garrison started seeing a lot of 3D printed gun parts in his work at the Sheriff’s department. It was mostly 80% kits and automatic conversion kits, small 3D printed pieces of plastic that turn a semiautomatic pistol into an automatic one. Then he got his first case with a fully 3D printed gun frame. “That’s when I was like, ‘We might need to know a little bit more about this now if we’re actually going to be seeing this stuff and potentially have to testify to it,” he told 404 Media.
A few years later Garrison attended a conference for forensic examiners in Atalanta and caught a talk by FBI lab tech Corey Scott. Scott had been 3D printing novelty items and noticed something. “He was just like, ‘Hey, I noticed on these 3D printed items, there’s these marks, but we was like: ‘I’m not actually a firearms or toolmark examiner.’”
A toolmark is a consistent scratch or impression a harder object leaves on a softer one. A screwdriver may produce the same scratches in the head of every screw it touches. A pair of bolt cutters will scratch up a length of chain in the same way every time. Matching tools to the objects they interacted with is one of the bedmarks of forensic science and it’s something Garrison is an expert in. So the question was: do 3D printers leave behind consistent toolmarks on the objects they make? When he got back to his San Bernardino lab following the conference, Garrison put the 3D printed weapon frame under the microscope. He noticed that the manufacturing process had left stria, or scratch marks, behind. If a 3D printer left behind the same pattern of stria on everything it printed then it might be possible to match a printer to an object it printed.
From there, Garrison started printing simple blocks at home on his own 3D printer. He’d take them into the lab on his own time and examine them under a microscope. “That’s when I started seeing some of the consistency on two separate printed things,” he said. It was too early to tell, and it’s still too early to tell, but individual printers might leave behind unique toolmarks on every object they print.
A page from 'An exploratory study of topographical signatures within 3D fused deposition modelling using Polylactic Acid (PLA) filament.'
Most 3D printers work by heating up a filament—often, but not always, plastic—and extruding it through a metal nozzle. The nozzle puts down hundreds, or even thousands, of layers of the heated plastic to form a solid object. Each individual level of the print is called the print line. “So on the firearm, I’m seeing from the trigger guard—maybe print line 200—and the top of the magazine well—print line 400—the marks are staying consistent,” Garrison said.
It was an exciting discovery but it also wouldn’t be admissible as evidence in a criminal trial. Despite the promise that we may one day be able to match a printer to the object that made it, Garrison stressed that the work was in its very early days and that it would take years, perhaps even a decade, of science to work out the truth of toolmarks and 3D printers.
He was also studying this on his own time and still had a full caseload with the Sheriff’s department. Garrison published a study about his results in the Forensics Science International that he co-authored with researcher Steven Pavlovich, but he knew there was more to do. “I’ve always been like, ‘Hey, someone who works at a university who gets paid to do this, you should totally do this right now,’” he said.
Enter Eric Law, an Assistant Professor at the University of Central Oklahoma Forensic Science Institute, and his graduate student Cooper Blair. Along with Garrison, the pair are the authors of a forthcoming research paper about the phenomenon of toolmarks in 3D printed objects. Once published, it’ll be the first of its kind.
Law and Blair’s focus is narrow. “So if we had a single printer and we had multiple nozzles, can we tell the difference between something printed on each of those different nozzles? And also, if we have different print bed surfaces, can we differentiate those print bed surfaces and tell what object was printed on which?” Law told 404 Media.
The nozzles used in 3D printing are often, but not always, made of metal and printed onto a strip of material that’s called a print sheet or print bed. They studied print sheets first. Not all sheets are the same, some are smooth, some are textured, and they come in a variety of different materials. “So we looked at textured, because we figured if there's some texture to it, those characteristics might reproduce on the plastic, and might let us do that comparison a bit easier,” Law said. “So I looked at texture print beds, and we could differentiate those 100% of the time.” Meaning that, both by eye and using a computer, his team could match an object to the sheet it was printed on.
It’s a promising early finding. “The problem we get into there is we're looking at a specific area on the print bed, so you have to print something on the exact same region, because every area on that print bed is different,” Law said. “If we print something right in the center and then print that same object in the top right corner, those would be different from each other. So it has to be in the same location, which complicates things a little bit.”
He pointed to Glock switches, the conversion kits that turn a pistol into an automatic weapon. “Those are pretty small and on a 3D print bed you could align a bunch of those and print them all at once,” he said. “Which is what you would do to produce as many as you can, as quickly as you can. If you had two of those they might look like they're from different printers, but they might have just been from different sections of the same printer.”
Print sheets can also move between printers and can be easily discarded. Knowing that a Glock switch was printed out on a particular sheet is not a smoking gun. “So it shows promise. But there's a lot of potential issues too,” Law said.
Law and Blair succeeded in matching nozzles to printed objects in their study, but the results weren’t as promising as the print sheets. Law said the nozzle match rate was correct about 75 percent of the time. “The algorithm could identify the correct nozzles, probably a little bit less than that with just visual examination,” he said. “It still shows promise, but is a bit more challenging.”
There are other issues too. All of Law and Blair’s tests were done with one kind of 3D printer—a Prusa MK4S. There’s hundreds of different devices on the market that all behave differently. Law also pointed out that brass nozzles warp over time themselves and may produce different results after hundreds of prints and that different nozzles made from different materials may work very differently. Law would also want an examiner rate study—a formal scientific inquiry into false positives and examiner bias.
“There’s a lot of promise in what we’ve seen but there’s also a lot of questions still. Different nozzles, different print beds, how easy it is to swap those and whether they change,” Law said. He would not, at this point, be willing to testify in a criminal case as an expert on 3D printed forensics.
Garrison also said he wouldn’t be comfortable using any of this in a court but he was still excited. “Even if it doesn’t work, and this is not a possibility, we still found out new information. I’d be just as happy with that. ‘Hey cool, I was involved in finding out that you can’t do this,’” he said.
Tom's Hardware: Ghost gun proliferation spurs crackdown at Thingiverse, the world's largest 3D printer model file repository — lawmakers also ask 3D printer vendors to create AI-based systems to detect and block gun prints (archive)
By Ash Hill published 2025-07-20 14:50:00 UTC
Thingiverse is cracking down on gun-related models using a new automated system.
As much as we love 3D printing, there's no denying the dangerous potential that comes with something like a modern 3D printer. Creating a weapon is as easy as loading a print file in your print queue, which is why big companies like Thingiverse have taken action to make the file acquisition process as hard as possible on their part. According to ABC, Thingiverse is now implementing a new strategy to stop users from uploading things like gun-related files before they're openly distributed on the platform.
This effort comes in response to an investigation handled by the New York Police Department (NYPD). The NYPD came across hundreds of weapon-related files on Thingiverse that could be downloaded by users and presumably 3D printed. Thingiverse is one of the largest websites for downloading 3D printable model files. ABC argues its rapid growth and subsequent jump in scale made it harder for the team to regulate these types of files.
The lack of control made it difficult for the team to manage, which led to the results found in the NYPD investigation. Thingiverse is now responding with a new "automated technology" designed to block the upload of dangerous files, like guns and gun-related components, before they're published.
The powers behind the movement at the District Attorney's office in New York confirm that they do not expect this effort to eradicate ghost guns. They do, however, want to make the process of finding ghost gun files as hard as possible and have decided to address one of the biggest sources for 3D printable CAD files in their efforts to help make that happen.
Manhattan District Attorney Alvin Bragg also contacted 3D printer companies like Bambu Lab, requesting they join in efforts to add hurdles to users who want to 3D print guns and gun-related components. Bragg requested Bambu Lab consider implementing an AI-driven system that checks CAD files against a model trained on gun blueprints to automatically detect gun-shaped parts.
If you're new to 3D printing, check out our list of the best 3D printers to see which devices we recommend. We don't recommend 3D printing any weapons, and already tried 3D printing a gun for ourselves if you want to see how that turned out.
