DNA transfer to worn upper garments during different activities and contacts: An inter-laboratory study

Cellular material derived from contact traces can be transferred via many direct and indirect routes, with the manner of contact and the time of transfer (in relation to the alleged crime-event) having an impact on whether DNA is recovered from the surface and a reportable profile generated. In an effort to acquire information on the transfer and recovery of DNA traces from clothing items worn during scenarios commonly encountered in casework, upper garments were worn during a normal working day before individuals were paired to embrace one another ('contact'), go on an outing together ('close proximity'), or individually asked to spend a day in another person's environment ('physical absence'). Each prescribed activity was repeated by sixteen individuals across four countries, and was the last activity performed before the garment was removed. Samples were collected from several areas of the upper garments and processed from DNA extraction through to profiling within the laboratory of the country in which the individual resided. Activities relating to the garment prior to and during wearing, including the prescribed activity, were recorded by the participant and considered during the interpretation of results. In addition to obtaining reference profiles from the wearer and their activity partner, DNA profiles from the wearers' close associates identified in the questionnaire were obtained to assess the impact of background DNA transferred prior to the prescribed activity. The wearer was typically, but not always, observed as the major contributor to the profiles obtained. DNA from the activity partner was observed on several areas of the garment following the embrace and after temporarily occupying another person's space. Particular areas of the garment were more prone to acquiring the hugging partner or office owner's DNA than others, and whether they were observed as the major or minor component was activity dependent. For each of the pairs, no DNA from the activity partner was acquired by the garments during the outing, even though both participants were in close proximity. This study provides empirical data on the transfer, persistence, prevalence and recovery of DNA from clothing items, and enables a better understanding of the mechanisms which lead to the transfer and detectability of DNA traces in different scenarios.