DNA recovery from 3D printed firearms

Over the last few years, additive manufacturing, by means of fused deposition modelling 3D printing, has become increasingly popular and accessible due to the relative low costs, flexibility, and continually lowering barriers for entry. Unfortunately, while this technology is not only used by hobbyists for creative or practical creation of custom objects using a variety of thermoplastic materials, they can also be used in the manufacture of firearms. From fully printed to hybrid designs, AM/3D printing has been used to produce parts for fully functional firearms capable of discharging conventional ammunition. The designs for such firearms can be easily found, downloaded and shared from the internet with 'enthusiasts' developing ever more sophisticated designs. In environments where lawful possession of firearms is strongly controlled, the ability to manufacture and assemble firearms through 3D printing technologies presents an increasing challenge for law enforcement, especially for forensic units tasked with collection, examination and recovery of evidence from these items. Forensic examination of 3D printed firearms can require a different approach compared to conventional firearms if maximum forensic intelligence is desired. Due to the decentralised and often individual nature of manufacture, biometric identification of both the handler/possessor and the manufacturer/assembler of the firearm can have investigative value. However, this can present a dilemma, as collection of biometric evidence from internal surfaces of the firearm typically requires dismantling of components which may affect functionality in subsequent test firing processes. This study aims to investigate DNA transfer and recovery on 3D printed firearms (Harlot pistols and FGC-9) in casework-inspired handling scenarios, to determine the most probative regions for the recovery of DNA originating from the assembler and handler of such firearms as well as determining the effect of firing (or test-firing) the firearm. The findings suggest that assembler DNA can be recovered from internal surfaces of the firearms, with significantly more DNA recovered from internal grip pieces than internal triggers. Further, the proportions of assembler DNA recovered on internal surfaces were significantly more than the proportions on external surfaces, based on contributor proportion percentages. In this study, test firing of the firearm, even up to 25 times, did not result in detectable DNA relocation onto internal surfaces from the individual conducting the test fires.