Background Levels of Salivary‐α‐amylase Plus Foreign DNA in Cases of Oral Intercourse: a Female Perspective

Abstract

Saliva plus DNA from a suspect is commonly encountered in sexual assault cases on bodily swabs. However, without background knowledge, the weight of this evidence is unknown. It may indicate the presence of saliva resulting from cunnilingus, or it may represent indirect transfer. In this study, females who refrained from cunnilingus donated 43 items of underwear and 19 vaginal swabs. The samples were subjected to Phadebas(®) , RSID(™) -Saliva and mRNA profiling and were subsequently DNA-profiled to determine the prevalence of background saliva in the female population. The results report that 15.8% of females who refrained from cunnilingus were positive for saliva and a further 10.5% also had DNA from unknown source(s). These findings of the rate of indirect transfer were evaluated with the Bayesian approach, and it was found that the evidence of saliva plus a high foreign DNA source adds moderately strong support to the allegation of cunnilingus.

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

“…Thus, it is recommended that positive results on Phadebas® paper should not be assigned a class of origin based on the Phadebas® Forensic Press Test alone. To further enforce this recommendation, it has been shown in two studies [3,4], that only a rather small proportion (13%) of items that exhibit positive indications for saliva with Phadebas® paper, return positive results with the confirmatory test Rapid Stain Identification Saliva (RSID™-Saliva).…”

“…The forensic significance of saliva is often understated, yet the primary source of deoxyribonucleic acid (DNA) evidence recovered from volume crime scenes as reported in the United Kingdom arises from saliva, typically located on peripheral items such as drinking vessels and cigarette ends [2]. Furthermore, establishing the nature of, and involvement in a physical or sexual assault may rely on the detection of saliva on exhibits such as swabs, clothing or bedding from actions such as biting, saliva expectoration or oral intercourse [3,4]. Regardless of the means by which saliva becomes deposited at crime scenes or on exhibits, the practising forensic scientist is faced with one fundamental issue; the detection (or more specifically the localisation) of saliva.…”

A template for constructing Bayesian networks in forensic biology cases when considering activity level propositions

“…There have been numerous publications demonstrating the importance of considering activity level propositions when evaluating forensic results [4,[13][14][15][16][17][18][19][20][21], and certifying (online) courses focusing on activity level evaluation of forensic findings are now available [22]. These developments reflect a tendency towards a broader recognition and acceptance of evaluations of findings given activity level propositions amongst the forensic community (and specifically, as is the focus of our paper, the forensic biology community).…”

The importance of male underwear in cases of alleged sexual assault

“…The Phadebas press test (Magle Life Sciences-Lund, Sweden) was used to screen for α-amylase and was carried out as per manufacturer's instructions [13,14]. Areas in which a color change was observed within 40 min were marked, and a small area was then cut out for RSID™-Saliva testing (Independent Forensics Ltd.), which was carried out as per manufacturer's instructions [15].…”