A model research study on persistence, recovery and analysis of trace DNA under fingernails of drowned bodies

DNA obtained from the crime scene or in the form of trace evidence is one of the most crucial pieces of evidence to individualize an assailant. During a violent physical assault, DNA, in the form of epithelial cells or blood due to violent scratching, is deposited in the hyponychium of the fingernail. This trace DNA is recovered and extracted from the fingernail debris by nail swabbing, and genetic profiling is done from the extracted DNA. The objective of the study is to evaluate the amount of exogenous DNA that persists in fingernail debris and the difference in recovery rate of the biological material under fingernails after specific time intervals while immersed in different water bodies. The study uses synthetic/prosthetic fingers that mimics the real-life drowned cases. Among the three different water bodies included in the study, samples recovered from tap water were highest in concentration; with a concentration of approximately 21 ng/µL even after 48 h of submersion. Whereas, the lowest concentrations of DNA, as low as 0.68 ng/µL, were observed in samples that were recovered from the sewage water after 48 h of submersion. The findings revealed that DNA yield varies significantly depending on the type of water body, with freshwater environments (tap water and canal water) showing higher recovery rates compared to polluted waters (sewage water). These results are pivotal in understanding the potential of fingernail debris as a forensic sample for DNA analysis, particularly in the cases of drowning. The use of prosthetic fingers in this study provides a controlled and ethical model that can simulate submersion scenarios and help inform forensic protocols for evidence collection in real-world drowning or submerged body cases.