Illicit substances are frequently distributed in zip lock bags. When these are seized by investigators, forensic examiners look for fingerprints and DNA that could link the drugs to an individual.
Now, a new study from researchers at Flinders University aims to guide investigators on which area of the plastic bag may be most informative when sampling for DNA.
The study showed that the contact made during the construction of drug capsules yielded enough DNA for complete DNA profiles from all the samples tested, while simultaneously allowing for secondary transfer of DNA. This secondary transfer was observed on the inside surface of storage containers and inside packaging materials. The exterior surface of the zip lock bags often yielded mixtures, with the individual making direct contact not always the major contributor to DNA profiles generated. However, the researchers found that the act of packing capsules into bags—despite direct contact with the bags and capsules—can provide little to no DNA from the person responsible.
Capsule makers, packers and transporters
The study used a three-person chain to 1) make capsules; 2) pack capsules into bags; and 3) possess and transfer the bags. The 3-step process completed five times per chain with two zip lock bags at a time, giving a total of 10 bags per chain.
The zip lock bags were then sampled for DNA on the inside, the inner semi-protected portion of the opening, and the outside surface. The exterior of capsules was also sampled along with a storage container. The sample size of 10 zip lock bags, 10–20 capsules and five containers per chain led to 110 DNA quantification data and 90 STR profiles.
According to the study results, published in FSI: Genetics, the capsule maker’s DNA was detected as the major or only contributor in 100% of DNA profiles generated from the capsules. The likelihood ratio values were greater than 100 billion. Similarly, the capsule maker’s DNA was detected on the inside of the bag in 90% of samples, with all of the samples having LR values in excess of 100 billion also.
However, despite direct contact with the outside and zip area of the bag and the capsules themselves, the capsule packer left little to no DNA on these areas. Of the 30 sampling areas (10 each of outside, zip area and capsules) directly touched by the capsule packer, their DNA was only detected in 6.7% of the samples—both from the zip area—with a maximum LR value of 25. The capsule packer’s DNA was not detected on any of the capsule samples even after direct contact during packaging.
The transporter reported touching the zip lock bags an average of 14 times over a 4-day period. The outside of the bag yielded the greatest amount of DNA, while the zip area had the lowest. The outer surface of the bags were handled by the transporter with the potential to have non-self-DNA transferred onto the bags. Only the capsule packer should have had the opportunity to make direct contact with the zip area. Despite this, DNA from the transporter was detected in the bag’s zip area in eight samples. They were the major contributor in 50% of zip area samples.
The study results suggest that the inside of the bags and exterior of the capsules could be targeted to identify individuals involved in the early packaging stages of the illicit drug pathway, while the outside could provide more information on recent handling.
“This small-scale study indicates that capsule packers deposit less DNA than capsule makers who spend more time handling drug casing, and those that make the capsules can leave enough DNA for a complete profile with as little as 30 seconds of contact,” said Flinders Ph.D. candidate Madison Nolan, lead author of the study.