UC Davis

With an increase in the number of crimes associated with firearms, firearms being directlyhandled by individuals involved in criminal activities, serve as a vital source of DNA providing a direct link between suspects and crime scenes. The common source of DNA analysed from a firearm related crime scene are guns, which contain contact/touch DNA. Touch DNA refers to DNA left behind on surfaces or objects by an individual through skin cells or bodily fluids. Although touch DNA collection is non- invasive, the low amount of DNA present requires high sensitivity and specificity in the collection, extraction, and quantification methods. However, there are several challenges and limitations to this approach. This study aimed at exploring techniques for recovering DNA from firearm surfaces for sample preparation, collection, extraction, quantification and to highlight the importance of optimized methods for DNA recovery and analysis to aid in forensic investigations. To ensure reliable results domesticated fingerprint (DFP) technique which is a technique that focuses on eliminating DNA content variability in human fingerprints was applied. The DFP contained a known quantity of DNA in a background of fingerprint chemistry, and this way DNA recovery could be quantified for parts of the firearm used in the study. DNA loss/recovery at key fail points was quantified using qPCR for firearm surfaces such as casings and triggers. The results were analysed using statistical measures, including mean, and standard deviation, to validate the findings. While DNA recovery/loss values from casings were statistically validated, recovery/loss values from triggers were not statistically significant due to operational errors. In conclusion, this research serves as the first step in addressing a wide range of challenges associated with touch DNA interactions on firearms.