Impact of biological evidences on DNA profiling of sexual assault cases

The identification of perpetrator involved in crime becomes difficult due to lack of evidence. Biological evidence plays an integral role in establishing link between survivor, suspect, and the scene of crime. The era of eye witness is almost diminished and DNA analysis is necessary for the identification of perpetrator. The loss or degradation of biological traces due to urinating, defecating, douching of genitals, showering and delay in medico-legal examination may yield negative results. The objective of study was to link DNA profiles generated from biological samples to associate suspect with survivor and other parameters affecting the results of DNA profiling. This present study was conducted in the Biology & Serology Division of Regional Forensic Science Laboratory, Northern Range, Dharamshala and DNA Division of State Forensic Science Laboratory, Himachal Pradesh, Junga, India. A total of 142 sexual assault cases received for examination during the year 2018 and 2019 were studied. Human spermatozoa were detected in 39 (27.46%) cases and genetic profiles were generated. Spermatozoa were detected even after taking bath and washing of clothes in 3 (2.11%) cases. 10 (7.04%) survivors were menstruating at the time of assault. Hymen was absent in 43 (30.28%) cases followed by old healed tags in 37 (26.06%), recent tears in 15 (10.56%), intact in 9 (6.34%) and partially ruptured in 4 (2.82%) cases. Out of 39 cases, DNA profile resulted as an inclusion of assailant in 27 (19.01%) cases and exclusion in 12 (8.45%) cases. The persistence of spermatozoa on vaginal swabs was found up to 4 days. Only 18 (12.68%) survivors underwent medico-legal examination on first day of assault. The findings clearly showed that early medico-legal examination is of paramount importance to avoid the potential loss of evidence, which directly affects the results of DNA profiling.