A rape case with multiple unknown perpetrators

Abstract

Regular case work on sexual assaults, with one or multiple perpetrators, is challenging as such cases have many different aspects to take into account. Often, the limitations is due to the time frame between the alleged assault and the sample collection, the victim's activities in this time period, samples or clothing collected and the lack of reference samples from the victim, sexual partners, or the alleged perpetrator(s). Literature has shown that there are a correlation between the acid phosphatase reaction/seminal fluid or detection of spermatozoa and the time frame between deposition and sample collection [1–4]. However, we do not know whether the seminal fluid and amount of spermatozoa detected are evenly distributed throughout a stain, and if or how the sampling affects the DNA-results, especially in complex mixtures.In this sexual assault case, from 2011, the exhibits and body samples were first routinely investigated. The presumptive test (acid phosphatase Brentamine) produced positive reactions on all exhibits. Numerous spermatozoa were observed by microscopy in all collected samples. All fractions were analyzed using AmpFlSTR® SGM Plus kit (Applied Biosystems). Further, both ESX 17® kit (Promega) and Yfiler® kit (Applied Biosystems) were used for a selection of the sperm fractions.The results of all the analyzed sperm fractions showed complex DNA mixtures, with at least three and/or four contributors, in different mixture ratios. By using the different mixture proportions and deconvolution the DNA-profiles of two contributors could be deduced for all markers. A database search produced an “offender hit” for one of these profiles. As a final remark, the results in this case show that the sampling can be essential, and that the distribution of spermatozoa is not evenly distributed throughout a stain. The results indicate that it may be recommended to select several samples from the stain(s) in cases with multiple perpetrators and complex DNA-results.