Systematic analysis of decadactylar subungueal genetic traces in murder cases

Abstract

Foreign biological material under the fingernails of a murder victim and/or suspect can be valuable evidence in a criminal investigation. The aim of this study was to evaluate the prevalence of foreign DNA under each fingernail of victims of violent deaths, including fatal struggle or rape cases. Fingernail swabs or, alternatively clipping nails, were taken from all fingers of both right and left hands from 46 victims (13 females and 33 males) and treated separately. Semi-automated DNA extraction was performed and 21 markers were genotyped. We detected reliable profiles in all the studied samples (n = 460). The majority of results produced a single profile that matched the donor. Foreign DNA was detected in 15/46 victims, 61.5% positive detection in females vs 21.2% in males. A total of 38/390 DNA mixtures were detected in biological material under the fingernails being 19 from right hand (50%) and 19 from left hand (50%). The finger-like distribution was similar in right and left hands where the index, middle and ring fingers showed the 86.8% of the positive results; being these findings in line with the strength and shape of hand's fingers. The sample treatment optimization increased the possibilities of obtaining biological material from the perpetrator being a powerful tool in a murder investigation. Processing strategy including the penta-dactylar analysis of each hand for independent subungueal recovery of informative exogenous genetic material by fingernail clipping or swabbing and the use of optimized extraction and purification protocols might increase the rate of success in identifying criminal felons.