Trace DNA Transfer in Co-Working Spaces: The Importance of Background DNA Analysis

Abstract

The presence of background DNA (bgDNA) can hinder the evaluation of DNA evidence at the activity level, especially when the suspect is expected to be retrieved due to their habitual occupation of the investigated environment. Based on real-life casework circumstances, this study investigates the prevalence, composition, origin, and probable transfer routes of bgDNA found on personal items in situations where their owner and person of interest (POI) share the same workspace. Baseline values of bgDNA were evaluated on the participants' personal items. Secondary and higher degree transfer scenarios of non-self DNA deposition were also investigated. The DNA from co-workers and co-inhabiting partners can be recovered from an individual's personal belongings. Non-self DNA present on the hands and deposited on a sterile surface can generate uninformative profiles. The accumulation of foreign DNA on surfaces over time appears to be crucial for the recovery of comparable profiles, resulting in detectable further transfer onto other surfaces. For a thorough evaluation of touch DNA traces at the activity level, it is necessary to collect information not only about DNA transfer probabilities but also about the presence of the POI as part of the 'baseline' bgDNA of the substrates involved.

Keywords: DNA transfer; background DNA; co-worker; forensic; non-self DNA; office; partner; prevalence; touch DNA.

Figure 1

Graphical representation of the results of Part B of this study, concerning the direct handling of sterile credit cards by the participants for the evaluation of inter- and intra-individual variation in shedding propensity. On the left, the DNA amount (ng in 30 μL) deposited on the cards is reported, while on the right, the respective profile completeness of the donor of the trace (O) is reported. Mean values are marked as red dots and their numerical value is reported in the boxplots.