Isolation and identification of female DNA on postcoital penile swabs

Background levels of body fluids and DNA on the shaft of the penis and associated underpants in the absence of sexual activity

This study examines the background of blood, saliva, semen and autosomal DNA on penile swabs and underpants from males in the absence of recent sexual activity. Based on the data collected by the AFSP Body Fluid Forum, the results of this study show that; there is a very low expectation of detecting blood on penile swabs and male underpants; a low expectation of detecting saliva on penile swabs and male underpants; and spermatozoa would be expected in less than a quarter of penile swabs and three quarters of male underpants. As none of the samples had detectable levels of DNA which were suitable for meaningful comparison that did not match the donor or their partner, the expectation of detecting a DNA profile from the cellular background on penile swabs or underpants from a male who has not been involved in recent sexual intercourse is very low. The results of this study are extremely informative when evaluating the significance of blood, saliva, semen and DNA detected on the penile swabs and underpants of males in cases of alleged sexual assault.

Transfer, persistence and recovery of DNA and mRNA vaginal mucosa markers after intimate and social contact with Bayesian network analysis for activity level reporting

In sexual assault cases, it can be challenging to identify the type of body fluids/ cell types present in a crime scene sample, especially the origin of epithelial cells. Therefore, more labs are applying mRNA body fluid analysis for saliva, skin and vaginal mucosa markers. To address activity level propositions, it is necessary to assign probabilities of transfer, persistence, prevalence and recovery of DNA and mRNA markers. In this study we analysed 158 samples (fingernail swabs, penile swabs and boxershorts) from 12 couples collected at different time points post intimate contact and after non-intimate contact in order to detect DNA from the person of interest (POI) and mRNA vaginal mucosa markers. Samples were DNA and RNA co-extracted and analysed with PowerPlex®Fusion 6C System and 19-plex mRNA primer mix respectively, using Endpoint PCR and the CE platform. Vaginal mucosa was detected up to 36 h post intimate contact, but also detected in one non-intimate contact sample. In 94% of intimate contact and 50 % of non-intimate contact samples the DNA results support the proposition that POI is the donor (LR ≥ 10,000). There was a strong association between the detection of vaginal mucosa and the average RFU value of the POI. The data were used to instantiate a comprehensive Bayesian network to evaluate the evidence at activity level, given alternate propositions conditioned upon indirect or direct transfer events. It is shown that the value of the evidence is mainly affected by the high DNA quantity (measured as mean RFU) that is recovered from the POI. The detection of vaginal mucosa had low impact upon the resultant likelihood ratio.

A retrospective study on the transfer, persistence and recovery of sperm and epithelial cells in samples collected in sexual assault casework

Data from all sexual assault cases analysed at the Section of Forensic Biology at Oslo University Hospital in the period 2013-2015 were reviewed to study transfer and persistence of cells deposited on the body. Data were recorded on detection of both sperm and epithelial cells. The final dataset consist of 2141 samples from 765 cases. In this study "positive findings" refer to evidence to support the proposition that the DNA profile was contributed by the POI and do not only correspond to detection of cell type, e.g. sperm cells. Positive findings from analysis of sperm cells could be detected in samples collected up to 72 h after deposition, and was less frequently detected in oral swabs were the longest observed persistence time was 12 h. Positive findings from analysis of epithelial cells were observed up to 43 h after deposition. A high success rate was observed from penile swabs collected within 24 h of the incidence demonstrating the importance of collecting and analysing such samples in cases where no semen is detected.

DNA transfer through nonintimate social contact

The UK and Ireland Association of Forensic Science Providers' (AFSP) Body Fluid Forum (BFF) set out to assist in the interpretation of sexual offence cases where semen is absent on vaginal swabs but female DNA is present on penile swabs or male underwear, and the issue to be addressed is whether or not sexual intercourse occurred. This study aims to investigate the frequency and amount of female DNA transferred to the penis and underwear of males following staged nonintimate social contact with females and to compare the findings with the amount of female DNA transferred to the penis and subsequently to the underwear of a male who had engaged in unprotected sexual intercourse with a female. In this study, no matching female DNA was detected on the inside front of the 44 items of male underwear used in this research following staged contact of a nonintimate nature and subsequent secondary transfer to the penis. After sexual intercourse, full profiles matching the female participant were found on the inside front of the males underwear with maximum peak heights in the range between 1898 and 3157 rfu. It was possible to demonstrate that DNA can occasionally transfer to the waistband and outside front of underwear worn by a male following staged nonintimate social contact. Data obtained in this study suggest that a matching female DNA profile below a peak height of 1000 rfu on the waistband of a male's underwear might be explained by nonintimate social contact with secondary transfer of female DNA from the male's hands.

The detection of female DNA from the penis in sexual assault cases

An investigation was performed with the aim of assessing the success rate of the examination of penile swabs or imprints for the detection of the female DNA profile. Two hundred twenty seven cases from a 3-year period were retrospectively reviewed. In 57% of the cases, no suitable material was available. Of the remaining 97 cases, 26 provided a DNA profile from the female victim. It is concluded that although the total success rate is low, it is worthwhile performing the examination, especially if there is a short interval between the alleged sexual assault and the examination.