Impact of the Post-deposition Interval on Male DNA Recovery from Female Skin in Forensic Investigations

Abstract Purpose Crime scene investigations are time-sensitive, and delays in evidence recovery can critically impact forensic outcomes. This study examines the effect of post-depositional time on the integrity of male salivary DNA recovered from female skin, simulating real-world delays in sexual assault evidence collection. Methods Saliva samples from 10 couples were collected at five intervals: one, three, six, twelve, and eighteen hours post-deposition (n = 50). DNA was extracted using the MyPrep Forensic DNA Extraction Kit and profiled using the Ingenomics Y Profiler Kit targeting 38 Y-STR loci. Profile quality was assessed via total peak height and global colour balance, with statistical comparisons performed using the Kruskal-Wallis H test and Dunn's post hoc test with Bonferroni correction. Results Complete Y-STR profiles were obtained from all samples up to twelve hours, with no allele dropout. A statistically significant decline in profile quality was observed from six hours onward (p = 0.050), becoming most pronounced at eighteen hours (p < 0.001, η²=0.53). At eighteen hours, 80% of samples still yielded complete profiles, with dropout concentrated at medium and high amplicon loci. Conclusion Male Y-STR profiles can be successfully recovered from female skin up to twelve hours post-deposition, supporting the forensic utility of salivary DNA in delayed sexual assault reporting. Beyond twelve hours, progressive degradation reduces genotyping reliability, emphasizing the need for timely evidence collection.