In drug investigations, evidentiary items such as weapons, clothes and drug bags are commonly processed in search of trace DNA from illicit drug manufacturers and dealers. And while chemical drug profiling is incredibly common and successful, it can run into problems.
For example, when active ingredients are prepared in large batches, there is the possibility that multiple chemically identical profiles are present in the illicit drug marketplace—providing law enforcement no unique information they can track or leverage. That’s why Australian forensic scientists are turning to touch DNA.
“To reveal additional trafficking and networking detail, new approaches to the examination of drug preparations are required,” the researchers with Flinders University write in their new study.
While the new investigation is based on touch DNA, it’s ultimate focus is DNA found in a very specific place: drug capsules (or pills). The use of drug capsules for illicit drugs, especially ecstasy, has ridden steadily over the past 10 years. For example, according to Australia’s Ecstasy and Related Drugs Reporting System, capsules were used by 83% of drug-taking participants in 2020.
In the study, published in Forensic Science International: Genetics, two participants handled three types of drug capsules for 15 seconds. Before handling, the participants washed their hands without soap, and then touched the bottom and lid of a capsule for 15 seconds before joining them together and placing in a Ziplock bag. The two participants did this 10 times for each capsule type, with at least one hour between each sample.
Using PCR-based methodology that is common in most of today’s forensic DNA laboratories, the scientists recovered DNA quantities ranging from 0.006 to 3.700 ng, with an average of 0.267 ng. According to the study results, full profiles (46 alleles) were obtained for 25% of the 60 samples. The overall average number of donor alleles recovered was 30. Overall, 80% of profiles were classed as “informative” for donor alleles.
“The mean for all three types of capsules for both volunteers was above the 12 allele threshold, indicating that on average, regardless of the capsule type or individual, DNA in sufficient quantity was isolated from these capsules when touched for 15 seconds to generate an ‘informative’ profile,” explain the forensic research team, led by Flinders University’s Amy Griffin.
For inclusion of a participant by profile contributor, informative profiles had to produce likelihood ratios (LR) above 1 x 103. In total, 75% of samples produced LR values in excess of 1 × 106, while a further 7% produced an LR value between 1 × 103 and 1 × 106. Only 10% of samples had LR values below 1 that could not support inclusion as a profile contributor.
Both participants transferred DNA from other individuals to the capsules but, in every circumstance, the study donor was still found to be the major contributor in the mixtures.
Griffin and team say their preliminary study highlights the idea that further investigation into touch DNA on the exterior of drug capsules is warranted. They are already exploring the method in terms of how capsules are handled in realistic scenarios—more typical of what is encountered in casework.
Photo credit: Flinders University