The added value of trace DNA in an investigative context

Traces (remnants of a past event under scrutiny) provide a great deal of useful information, however many aspects of selection and recovery need further exploration. The increased use of trace DNA has prompted extensive research into recovery rates of DNA profiles from various surfaces and collection methods. While recovery rates inform trace targeting, the utility of a profile reflects its actual contribution to an investigation. Utility is defined as the added value the use of a trace provides to an investigation, which if measured would increase knowledge for trace selection and analysis. This project analysed 47,097 data points relating to trace DNA samples³ collected during 2022 within New South Wales, Australia. Recovery rates of these exhibits were calculated for comparison. Further, a subset of 1206 data points were analysed to ascertain the utility or added value of the trace DNA profiles found, i.e. did the recovered profile add value to the investigation? Results showed that when considering recovery and the added value of an exhibit collectively, trace DNA profiles from steering wheels, weapons, motorcycle or bikes, paper or porous items and plastic items demonstrated comparatively high performance. Items with high recovery rates such as clothing were seen to not add comparatively as much value to investigations. It was noted, however, that when clothing profiles did add value, there was a higher percentage of identifications to persons not previously connected to the investigation (defined as cold links), when compared to other exhibit types. This project developed and tested an integrated approach that considers profile recovery rates, the utility of a profile and the investigative context of traces. Together, these provide a more holistic, context-sensitive view of trace DNA effectiveness, supporting an initial decision-support framework to assist crime-scene officers in trace selection.