DNA evidence in illicit drug trafficking: A forensic analysis of transfer DNA between packaging materials

The illicit drug distribution pathway commonly involves powdered substances encapsulated and distributed in small plastic bags via multiple intermediaries. This study investigated the DNA transfer dynamics between individuals involved in the production, packaging, and transportation of such materials through two experimental pathways. In the first experimental design, we established a two-person chain wherein Participant A manufactured and packaged capsules into zip lock bags (ZLBs), which were subsequently transported by Participant C for a four-day period. The second experimental pathway involved a three-person chain: Participant A prepared the capsules, Participant B inserted them into ZLBs, and Participant C carried the packages. DNA sampling was conducted on multiple surfaces: the interior of the ZLBs, the semi-protected opening regions, the exterior surfaces, the capsule exteriors, and the storage containers. Forensic analysis employed Verifiler™ Plus for DNA profiling with subsequent data deconvolution using STRmix™ software. Results demonstrated that informative DNA profiles could be successfully recovered from capsules despite observable DNA transfer between capsules, storage containers, and bag interiors. The exterior surfaces of ZLBs yielded complex mixed profiles, whereas the more protected surfaces—bag interiors and capsule exteriors—typically produced profiles with predominantly one or two contributors. These findings have significant implications for forensic investigation strategies, suggesting that targeting the interior surfaces of packaging materials and capsule exteriors may provide more reliable identification of individuals involved in the initial stages of drug packaging, while exterior surfaces offer greater insight into recent handling events in the distribution chain.