Assessment of DNA Transfer on Drug Packages in Simulated Vehicular and Household Settings

Background: DNA evidence can play a critical role during the investigation of illicit drugs cases. A key challenge, however, is in determining whether DNA profiles recovered on the evidence items, such as drug packages, arise from direct handling or indirect transfer. Methods: In this respect, we simulated common drug offense scenarios where illicit drugs were discovered inside vehicular or household settings that can be linked to the suspect. DNA transfer was evaluated based on two hypothetical propositions: (1) the individual's DNA was directly deposited onto the mock drug packages through handling, or alternatively (2) DNA persisting on a particular surface had transferred onto the packages. For the direct transfer scenario, 15 participants were requested to pack the mock drug packages using their bare hands. For the indirect transfer scenario, DNA-free mock drug packages were placed at various locations in 15 vehicles and 15 bedrooms for different time intervals. Following each scenario, DNA samples were collected from multiple areas of the mock drug packages. DNA transfer was assessed based on quantification and profiling results, which were subsequently evaluated within a Bayesian network-based framework. Results: Higher DNA transfer frequencies onto the mock drug packages were observed in the direct-handling experiment compared to those from indirect transfer, suggesting that DNA transfer occurs to a higher degree from active contact. In direct-handling scenarios, the amount of DNA recovered from the handles of the carrier bags was much higher than that from the exterior bodies, indicating preferential DNA deposition at the contact areas. Conversely, the results from indirect transfer scenarios showed similar recovered DNA amounts between the handles and the exterior bodies of the carrier bags, with minimal transfer to the interior surfaces. These findings indicate that the likelihood of recovering DNA from specific areas of evidence items can be linked to the particular activities and transfer mechanisms involved. Conclusions: The findings of this study expand the empirical knowledge of DNA transfer processes across diverse forensic contexts.