With the prevalence of forensic science in popular media, offenders are becoming more forensically aware and can employ precautionary methods, such as cleaning used items or rubbing away fingermarks, to reduce their traces left at a crime scene.This study examined the effects of various cleaning methods on DNA persistence on commonly encountered casework exhibits, specifically knives and mugs. Aliquots of acellular DNA were added to the knife handles or mug rims, allowed to dry, and then the substrates were either sampled directly or were cleaned and then sampled. The plastic-and wood-handled knives were cleaned with a cloth in a sink of water, diluted dish washing liquid or diluted household bleach, whereas the ceramic, glass and steel mugs were cleaned with a dry or wet cloth, or by wiping with a cloth after applying a cleaning product (dish washing liquid or household bleach spray) directly into the mug and then rinsing it with water. DNA samples were collected with wet and dry swabs, in triplicate, and extracted and quantified. In both experiments, DNA was not detected on items after cleaning with dish washing liquid or household bleach, irrespective of the differences in amounts of DNA initially deposited, substrates, and cleaning methods. Even without a cleaning product, rubbing with a dry cloth decreased DNA recovery from the mugs, regardless of the mug substrate. These results contribute to our understanding of the impact of various cleaning methods on DNA recovery at the crime scene and will help inform DNA recovery strategies.

It is important to understand the variables impacting DNA persistence when considering the recovery, and evaluative interpretation, of DNA evidence from crime scenes. Whilst it is known that temperature, humidity and UV affect DNA persistence, little research has been conducted to explore these effects in a combined and controlled manner. This study includes two experiments in which a climate chamber was used to simulate climatic conditions over a repeating 24-hr period. Aliquots of ~50ng DNA were added to each substrate and DNA recovered at 0, 1, 3 and 7 days after deposition. Samples were run in triplicate, extracted and quantified. The first experiment investigated the effect of typical Southern English winter and summer days on DNA persistence on glass and cotton, with DNA being recovered by wet and dry swabs from glass and mini-tapes from cotton. The second experiment investigated the effect of typical Northern Italian winter and summer days on DNA persistence on cotton and polyester, with DNA being recovered by wet and moist swabs from both fabrics. Quantities of DNA on all substrates significantly declined over 7 days under summer conditions (p<0.05), and more DNA tended to persist on the fabric substrates in both studies under conditions of winter than summer. These results contribute to our understanding of DNA persistence under different climatic conditions and will help inform investigators' DNA recovery strategies.