Research paperAssessment of the transfer, persistence, prevalence and recovery of DNA traces from clothing: An inter-laboratory study on worn upper garments
Introduction
The ability to acquire DNA profiling data from various items collected at crime scenes and submitted as evidence has been demonstrated within forensic casework [1]. Among these items, clothing is commonly encountered and submitted for sampling, with the success of obtaining a profile varying among laboratories [[2], [3], [4], [5], [6]]. The garment area sampled appears to strongly impact the quantity and quality of DNA retrieved. Studies have demonstrated an increase in the likelihood of obtaining a DNA profile associated with the wearer when samples are obtained from areas directly in contact with the skin’s surface for prolonged periods, such as the internal collar and cuffs of worn clothing [2,4,7]. DNA retrieval is further impacted by the collection method applied [8,9], though the use of sampling techniques appropriate to the substrate has been shown to improve DNA collection and the possibility of obtaining an informative DNA profile [10,11]. Furthermore, analytical methods applied by different laboratories, from extraction through to profiling, influence the quantity of DNA retrieved as well as the reportability and composition of the profiles generated [12], while laboratory-specific interpretation guidelines and procedures of DNA profiling results have been shown to have an effect on DNA profiling success rates [13,14].
Whilst the ability to obtain DNA profiles of sufficient quality for interpretation is crucial to the investigative process, appropriate targeting of the area is also key to obtaining profiles of probative value [15,16]. Unlike wearer DNA, which typically accumulates on clothing as a result of regular and/or prolonged contact directly with the surface of the skin during wearing, DNA from other individuals can also be directly and indirectly transferred to, and accumulate on, both internal [7,17] and external [[18], [19], [20]] areas of clothing worn during regular daily activities. Simulations focused on obtaining DNA from the perpetrator in attack [18], aggression [9], and grabbing and dragging [21,22] scenarios frequently detected DNA that could not be attributed to the wearer or perpetrator on external areas of worn clothing. Whether a result of direct or indirect contact with an individual, or through exposure to the surrounding environment, these studies demonstrate that background DNA, relative to the targeting of an individual (wearer or other), is typically collected during sampling and observed in the resultant DNA profile.
The level of background DNA present on clothing items, and to whom it can be attributed, is dependent on a number of factors centred around the activities performed prior to, during, and following wearing of the garment including how often the garment is washed (relative to wearing) and whether combined with items worn by others [21,[23], [24], [25]]; the handling and/or wearing of the item by an individual prior to or following wearing by another individual [4,[26], [27], [28]]; the shedder status of the wearer and individuals coming into contact with the clothing item [18,29]; regular interactions with individuals who are within close proximity to the garment/wearer [7,[18], [19], [20],24,30,31]; and interactions with items and surfaces on which DNA-containing material already resides [21]. In addition, the frequency and manner by which hands are used increases their possibility of being a vector for the transfer of foreign DNA between various surfaces, the wearer, and the garment being worn [[32], [33], [34]].
Given the routine collection of samples, and analysis of profiles, generated from clothing, it is of interest to determine how much DNA is collected from different areas of an upper garment, and who it belongs to, after normal wearing under different circumstances. This study aims to determine the frequency of detecting wearer and non-wearer DNA on upper garments worn on either working or non-working days and, in instances where non-wearer DNA was detected, whether it could be attributed to a close associate of the wearer. In addition to the collection of reference profiles of close associates, a core feature of this study was the collection of details concerning the activities performed and interactions between the participant, their associates, and the garment, prior to and during wearing. This information was taken into consideration during interpretation of the DNA findings.
As this study was performed within four different laboratories situated in four different locations around the world, the impact of inter-laboratory differences in the application of analytical methods on the data obtained was also considered in general terms; given the variation in lab-specific methodologies from collection through to profiling, it is not possible, nor was it the aim of this study, to determine which had the greatest impact on the results, or to assess overall laboratory performance. This study was devised to enhance our knowledge of the composition of profiles, and their probative value, obtained from different areas of a garment in order to assist scientists in making informed decisions on sampling strategy, as well as support inferences given activity level propositions [35,36].
Section snippets
Experimental design
Four ISO 17025 accredited laboratories situated in four countries participated in the study, referred to as Labs 1-4. As this project involved the use of human subjects, the work described has been carried out in accordance with the ethical requirements set out by the mandating body in each of the participating laboratories. Informed consent was obtained from those participating in this study and, in the case of minors under the age of 18, parental consent was provided.
Within each of the
Quality control
During sample processing, each of the laboratories included standard quality control procedures as per casework protocols. In general, controls performed as expected, with negative controls yielding no detectable DNA and positive controls resulting in the known genotype with no contaminating DNA detected. Replicate profiles obtained from a single negative control in Lab 2 displayed a small number of alleles with low peak-heights that were found to originate from the operator performing the
Concluding comments
The outcomes of this study expand the limited pool of available DNA-TPPR data and aid forensic examiners in obtaining meaningful profiling data through improved targeting. Considering the various routes of transfer to clothing items, we have found that DNA from the wearer is typically transferred to a garment as a result of direct contact through regular wearing, where it generally accumulates on internal surfaces such as the internal collar and cuff. Although good quality profiles
Funding
This study is part of the European Network of Forensic Science Institutes (ENFSI) ‘DNActivity’ project ‘Towards the Vision for European Forensic Science 2020 (TVEFS-2020)’ which is co-funded by the ‘Prevention of and Fight against Crime (ISEC)’ programme of the European Union under agreement number HOME/2013/ISEC/MO/ENFSI/4000005962. This project has been funded with support from the European Commission. This publication reflects the views only of the authors, and the European Commission or any
Acknowledgments
The authors would like to thank the volunteers and donors for their contribution to this study. We also thank the staff within each of the laboratories for their support with sample processing and profile interpretation, and the STRmix™ developers for their assistance with the settings and parameters required to interpret the profiles generated within this study. Special thanks to the biological examinations branch within Lab 4 for their assistance with profile interpretation and evaluation. We
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