Firearm-related crime represents a significant global challenge, and weapons recovered from crime scenes are routinely analysed for DNA to link individuals to shooting incidents. While traditional forensic DNA analysis addresses source-level hypotheses, modern casework increasingly requires activity-level evaluation. However, current knowledge regarding how different activities impact DNA deposition on firearms remains insufficient to fully support such assessments.

The aim of this study was to improve the understanding of how the amount and distribution of DNA on handguns are affected by relevant handling and storage scenarios. Direct transfer through loading and shooting was compared to secondary transfer via intermediate objects and interpersonal contact. Scripted scenarios related to loading and shooting were used to study direct transfer, while secondary transfer scenarios encompassed transport of the pistol wrapped in a used towel or placed in a bag with personal belongings. The experiments were conducted using both handguns and realistic replicas that were systematically cleaned using ethanol and bleach, with decontamination verified by qPCR. DNA was recovered through swabbing of multiple, non-overlapping areas such as trigger, grip, slide and magazine.

Different patterns of DNA distribution were observed depending on how the handgun had been handled by the depositor. Loading and shooting produced clear patterns of DNA deposits with the highest amounts on the grip, slide grip and magazine sides. Passive transfer from items, on the other hand, produced lower levels and more evenly distributed DNA traces across the surface of the pistol. The generated quantitative data can be used to support the interpretation of DNA findings under competing hypotheses about activities in casework and may ultimately contribute to more informed evaluation of evidence in court.

Authors

• Sofie Bergstrand (National Forensic Centre, Swedish Police Authority and Division of Biotechnology and Applied Microbiology, Department of Process and Life Science Engineering, Lund University, Sweden)
• Tomasz Dabrowski (Division of Biotechnology and Applied Microbiology, Department of Process and Life Science Engineering, Lund University, Sweden)
• Julia Bengtsson (National Forensic Centre, Swedish Police Authority and Division of Biotechnology and Applied Microbiology, Department of Process and Life Science Engineering, Lund University, Sweden)
• Johannes Hedman (National Forensic Centre, Swedish Police Authority and Division of Biotechnology and Applied Microbiology, Department of Process and Life Science Engineering, Lund University, Sweden)