Most conventional firearms come with serial numbers and leave unique microscopic markings on bullets and cartridge cases when fired. Investigators can use these clues to trace weapons or connect them to crimes. However, 3D-printed firearms, commonly called ghost guns, present a different challenge. They can be manufactured without serial numbers, and their unconventional construction can make traditional forensic analysis more difficult.
Now, researchers in Australia may have found another way to trace these weapons, using clues hidden in the plastic they’re made from.
The plastic itself could hold valuable clues
Researchers at Curtin University, working alongside forensic experts at ChemCentre, examined 28 samples of polylactic acid (PLA), a common 3D-printing plastic. They used a technique called differential scanning calorimetry, which measures how materials respond to heat. Interestingly, they could distinguish 26 of the 28 samples, including some that were identical in color but came from different manufacturers.
However, there was a problem. Plastic undergoes heating and cooling during printing, altering its thermal properties. Consequently, a finished object can behave differently from the original filament during testing. The researchers found a workaround. By subjecting both materials to controlled heating and cooling, they could account for those differences and successfully associate printed test pieces with their corresponding filament across 15 samples.
Could this finally help investigators trace ghost guns?
The technique could help police connect seized firearms to recovered printing materials or link weapons found in separate investigations, helping authorities advance an investigation.
Back in 2018, researchers developed a system called PrinTracker, which identified microscopic imperfections individual 3D printers leave on objects. It achieved 99.8% accuracy when matching printed keys to 14 test printers. Despite its promising results, PrinTracker has largely remained a proof of concept, partly because it requires a reference database of printers for comparison.
Curtin’s new approach could, in theory, help investigators compare plastic filament recovered from a suspect’s home or workshop with the material used in a seized 3D-printed gun, rather than relying on surface imperfections. That said, it is not yet ready as a full-fledged menthord to be used by law-enforcement yet. It still needs more testing, including with other materials and samples exposed to soil or water.
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