A Critical Evaluation of Touch DNA Recovery Methods for Forensic Purposes

Over the past decade there has been a significant increase in the number of submissions of touch DNA evidence to forensic laboratories. Previous research has indicated that analysis of these samples produces poor results, with only 5-6% of handled items generating a full profile (Quinones and Daniel, 2012). Published research, as well as case work review by forensic practitioners, has also indicated more consideration of how to improve the evidential value of touch DNA samples is needed. Therefore, this research aims to critically evaluate low-level DNA recovery and analysis methods in order to maximise efficiency for forensic identification purposes. Typical evidential items, such as plastic handled screwdrivers, aluminium cans, drinking glasses and wooden handles, were handled in a mock-operational trial. The deposited DNA was recovered from these items using a range of swabbing materials including cotton, polyester, nylon flocked, foam and rayon (also known as viscose). These samples were then quantified using human specific quantitative PCR and profiled using AmpFℓSTR™ NGM SElect™ and the RapidHIT™ 200 instrument. The DNA quantity and quality were compared and a statistically significant difference was found to be present between recovery methods from the different surfaces. The findings of this research allow for an optimal recovery strategy to be recommended based upon the surface type the DNA is being recovered from.

Additionally, it was determined that it is possible to analyse touch DNA evidence using Rapid DNA technologies which may provide great benefits to criminal investigations. The way in which the DNA interacts with the surfaces and the swabbing materials was also preliminarily evaluated to determine the impact this has upon the recovery efficiency of each recovery method. This research will inform best practice for the recovery and analysis of low-level DNA samples from forensic exhibits and can influence the ISO validation procedures for crime scene examination processes (ISO17020).