Illicit drugs are often packaged within multiple layers of packaging materials to evade detection during the trafficking process. When DNA evidence is recovered from these materials, a major challenge in forensic investigations is assessing whether the detected DNA originates from direct handling or indirect transfer. One of the more commonly encountered packaging materials in our laboratory is stretch film. Such film possesses distinct physical properties —high stretchability and elastic recovery, strong adhesion, and a tendency to accumulate electrostatic charges— that could facilitate mechanical capture and retention of biological materials from different individuals involved at different stages of drug packaging and trafficking. 

In this study, we simulated realistic drug trafficking scenarios where mock illicit drugs were packaged with plastic packets and stretch film. Twenty-eight participants were recruited and grouped into 14 pairs. In each pair, the first participant “A” used bare hands to prepare three identical mock drug packages by wrapping salt-filled plastic packets with stretch film, mimicking commonly encountered exhibits. One of the packed mock drug packages was examined to assess for direct DNA transfer during drug packaging. The remaining two packages were placed inside the personal bag of the paired participant “B”, i.e., “B” therefore plays the role of the “courier”. After 18-20 hours, one package from the bag was retrieved and examined, simulating the scenario of secondary DNA transfer during storage. For the other package, it was briefly handled (5-10 secs) by the bag owner “B” prior to examination to simulate the scenario of incidental contact. In these experiments, swabs were made from: 1) the exterior surface of the package prior to unravelling the stretch film, 2) the stretch film after it had been unravelled, and 3) the exterior surface of the salt-filled plastic packet. 

Our results showed that DNA attributable to the individual responsible for packaging (i.e., “A”) was recovered from most samples across all scenarios. In contrast, DNA from individuals whose bags were used to store the package (i.e., “B”) was detected less frequently on the stretch film, typically at lower relative contribution levels, and was not recovered from the plastic packets within the package. By comparing DNA profile compositions across different packaging layers, our findings underscore the varying evidential weight of DNA associated with distinct stages of illicit drugs handling, providing empirical data to support forensic practitioners in activity-level evaluation.

Authors

• Xiaoyang Li (DNA Profiling Laboratory, Biology Division, Health Sciences Authority, Singapore)
• Yong Sheng Lee (DNA Profiling Laboratory, Biology Division, Health Sciences Authority, Singapore)
• Nadira Binte Murad (DNA Profiling Laboratory, Biology Division, Health Sciences Authority, Singapore)
• Nur Ahda Binte Abdul Aziz (DNA Profiling Laboratory, Biology Division, Health Sciences Authority, Singapore)
• Ying Yin Loh (DNA Profiling Laboratory, Biology Division, Health Sciences Authority, Singapore)
• Christopher Kiu-Choong Syn (DNA Profiling Laboratory, Biology Division, Health Sciences Authority, Singapore)