Oral intercourse or secondary transfer? A Bayesian approach of salivary amylase and foreign DNA findings

The importance of male underwear in cases of alleged sexual assault

The potential evidential value of male underwear in cases of alleged sexual assault is often overlooked. Male underwear can be a critical item in the investigation of alleged sexual assaults. Body fluids/DNA, which may transfer to the penis during sexual contact, may in turn transfer to the inside front of the underwear, and persist for months or years, provided the underwear are not washed. Here, we demonstrate how the case circumstances drive the sampling strategy of male underwear, in order to maximize the effectiveness of the forensic analysis. Sampling considerations including recovery methods and sampling sequence are discussed, and a methodical examination strategy of male underwear is proposed. To highlight the pertinence of male underwear to the investigation of alleged sexual assaults, three real-life cases are discussed, in which male underwear were examined for multiple body fluids/DNA, and the findings obtained proved evidentially significant. The different cases demonstrate the versatility of male underwear examination in situations, where different body fluids and DNA may transfer based on the specific allegation, and emphasize how targeted sampling can allow the scientist to assess the probability of the findings based on two competing propositions. Accurate sampling strategies are imperative for robust probability assignment in evaluative reporting of scientific findings.

A spit in time: identification of saliva stains and assessment of total DNA recovery up to 180 days after deposition

The main aim of this work was to validate the detection of saliva samples from denim, cotton, and polyester fabrics aged up to six months, applying rapid immunochromatographic tests resulting in the analysis of nuclear and mitochondrial DNA recovered. A comparison was also carried out between two saliva detection tests, Laboratory and Crime Scene. 50 μl saliva samples (three per time and test) were deposited on denim, cotton, and polyester fabrics. After 1, 3, 7, 14, 21, 30, 60, 90, 150, and 180 days of storage at room temperature, the samples were recovered by swabbing and detected by SERATEC® Amylase (Laboratory) test and SERATEC® SALIVA CS (Crime Scene) test (SERATEC®, Göttingen, Germany). DNA was isolated from the swab extraction buffer applying a silica-based methodology, and quantified based on fluorescent and human-specific quantifications. Then, it was submitted to STR profiling and mtDNA sequencing. According to our results, saliva stains up to six months after deposition remain valid specimens. The intensity of the bands varied among fabric type and time. Total DNA was successfully recovered from all tested samples, though with the limitations of obtaining partial nuclear DNA profiles from the oldest samples. In contrast, complete characterization of mtDNA was achieved from all samples. Lab and CS tests performed similar on the detection of saliva, as well as, DNA yield and profiling. Future research will be able to expand these results, analyzing the stability of other body fluids and the sensitivity of rapid immunochromatographic tests to detect them.

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.

Assessing the background levels of body fluids on hands

Forensic scientists are often asked to assist the court by evaluating the significance of finding body fluids on the hands of an individual; however, there is an absence of published data regarding the background levels of body fluids on hands. Whilst the scientist can use casework experience to inform the courts on the significance of the results, it would be advantageous to have data which could assist with this interpretation. This study was designed to ascertain the background levels of blood, semen, saliva, hairs/fibres and staining/debris on hands in the general population by sampling from delegates attending a scientific conference. The findings suggest that approximately one third of the population would be expected to have hairs or fibres on their hands and that females are more likely to have visible staining on their hands than males. Presumptive tests for blood and semen yielded negative results in all samples; however, almost 2 % of the samples were found to contain a very low number of sperm heads. In contrast, the majority of samples tested positive for the presence of saliva using the presumptive Phadebas® amylase test. The data supports the caution applied by forensic practitioners when evaluating the presence of saliva detected using the presumptive Phadebas® amylase test based on the lack of specificity and indicates that the RSID™-Saliva test would be more suitable to use.

From crime scene to courtroom: A review of the current bioanalytical evidence workflows used in rape and sexual assault investigations in the United Kingdom

Sexual assault casework requires the collaboration of multiple agency staff to formalise an investigative pipeline running from crime scene to court. While the same could be said of many other forensic investigations, few require the additional support of health care staff and the combined forensic involvement of body-fluid examiners, DNA experts and analytical chemists. The sheer amount of collaborative effort between agencies is laid out through a detailed examination of the investigative workflow from crime scene to courtroom with each step in the pipelines detailed and discussed. Beginning with a review of sexual assault legislation in the United Kingdom this article details how sexual assault investigations are initiated by police and supported by sexual assault referral centre (SARC) staff who are often the first responders providing primary healthcare and patient support to victims while simultaneously collecting and assessing forensic evidence. Detailing the myriad of evidential material that can be documented and collected at the SARC, the review identifies and categorises key forensic tests to first detect and identify body-fluids recovered from evidence through to the secondary analysis of DNA to help identify the suspect. This review also focusses on the collection and analysis of biological material used to support the allegation that the sexual activity was non-consensual and provides a breakdown of common marks and trauma as well as a review of common analytical methods used to infer Drug Facilitated Sexual Assault (DFSA). The culmination of the investigative pipeline is discussed by reviewing the Rape and Serious Sexual Assault (RASSO) workflow used by the Crown Prosecution Service before providing our thoughts on the future of forensic analysis and possible changes to the described workflows.

The prevalence and persistence of saliva in vehicles

In forensic investigations involving stolen and crashed vehicles, examining airbags for the presence of saliva is useful strategy in order to try and establish who the driver of the vehicle may have been. The use of an evaluative approach in these types of investigations allows the forensic scientist to evaluate the significance of the evidence with regard to two alternative hypothesis. The presence of saliva on an airbag may be the result of the driver coming into contact with it during an impact. Alternatively, the saliva may have transferred to the airbag from another area in the vehicle following its deployment. To address this question and attach significance to this finding, a dataset on the prevalence and persistence of saliva is required, alongside relevant background information on the case. The purpose of this study was to determine if saliva matching the main driver of a vehicle is present in the areas immediately surrounding the driver's section, and also to determine the persistence of saliva in vehicles. Salivary-α-amylase was detected in 53% of all samples collected from vehicles. Saliva positive samples yielded statistically significantly (p<0.05) more DNA than saliva negative samples. There was no statistical difference in DNA yields from the different areas sampled in the vehicles. The steering wheel was observed to have the greatest number of saliva positive samples (80%). The driver's DNA profile was detected in 72% of the total samples taken. We demonstrated that saliva can persist for at least ten days in vehicles in daily use. This study has produced a useful dataset that can be utilised under certain conditions by forensic investigators when taking an evaluative approach to these particular types of forensic investigations.

Comparative performance of the Phadebas® Forensic Press Test at room temperature and 37 °C for the detection of saliva stains on fabric exhibits

The Phadebas® Forensic Press Test (PFPT) is an enzyme-based colorimetric test used to visualise and locate latent saliva stains on forensic exhibits. The test relies upon the presence of the enzyme α-amylase which is present in high levels in saliva. Even though the optimal in vitro temperature for α-amylase activity is 37 °C, the PFPT manufacturer's protocol specifies that the PFPT should be carried out at room temperature (RT). In this study, we compared the performance of the PFPT at RT and 37 °C using combinations of four fabric types (cotton, polyester, acrylic and a cotton/polyester blend), three saliva dilutions (neat, 1:10 and 1:100) and stains aged for four time periods (1 day, 1 week, 1 month and 3 months). The intensity of the PFPT colour reactions at RT and 37 °C were not statistically different across all fabric types, saliva concentrations and stain ages, indicating that maximum sensitivity and performance of the PFPT can be achieved at RT.

The evaluation and validation of Phadebas® paper as a presumptive screening tool for saliva on forensic exhibits

The Phadebas^® Forensic Press Test is routinely used for the detection of saliva. However, assessment of the use of Phadebas^® paper for this purpose has not been studied extensively. The suitability of Phadebas^® paper as a presumptive screening tool for saliva on forensic exhibits, was investigated by analysing the following: (1) sensitivity, (2) specificity, (3) effects of temperature on sensitivity and specificity, (4) detection of saliva in mixed body fluid samples, and (5) influence of substrate porosity. The results of this study demonstrated that Phadebas^® paper is more sensitive to α-amylase activity and less specific for saliva than previously reported. The use of an examination temperature of 37°C had no effect on sensitivity, but increased the incidence of cross-reactivity with other forensically relevant body fluid stains. Blood, urine and vaginal secretions can inhibit the detection of α-amylase activity with Phadebas^® paper in mixed stains of saliva and body fluid. Substrate porosity is a weak predictor for the time taken for a saliva stain to achieve a strong positive result on Phadebas^® paper. Overall, this study demonstrated that the Phadebas^® Forensic Press Test has limitations as a presumptive test for the accurate identification of saliva.

Cell type determination and association with the DNA donor

In forensic casework, evidence regarding the type of cell material contained in a stain can be crucial in determining what happened. For example, a DNA match in a sexual offense can become substantially more incriminating when there is evidence supporting that semen cells are present. Besides the question which cell types are present in a sample, also the question who donated what (association) is very relevant. This question is surprisingly difficult, even for stains with a single donor. The evidential value of a DNA profile needs to be combined with knowledge regarding the specificity and sensitivity of cell type tests. This, together with prior probabilities for the different donor-cell type combinations, determines the most likely combination. We present a Bayesian network that can assist in associating donors and cell types. A literature overview on the sensitivity and specificity of three cell type tests (PSA test for seminal fluid, RSID saliva and RSID semen) is helpful in assigning conditional probabilities. The Bayesian network is linked with a software package for interpreting mixed DNA profiles. This allows for a sensitivity analysis that shows to what extent the conclusion depends on the quantity of available research data. This can aid in making decisions regarding further research. It is shown that the common assumption that an individual (e.g. the victim) is one of the donors in a mixed DNA profile can have unwanted consequences for the association between donors and cell types.