In cases involving allegations of digital penetration of the vagina or anus, the Centre of Forensic Sciences conducts chemical testing for semen and saliva on the inside surface of underwear.  This approach is used to localize potential deposits of bodily fluids that may have been on the perpetrator’s hand at the time of the assault.  Cutouts are taken from corresponding locations when semen is detected, or the presence of saliva suggested or inconclusive, based on PhadebasTM testing. Cumulative casework experience and a review of recent literature have identified swabbing of the underwear, independent of any bodily fluid testing, as an approach that may lead to an increase in the number of cases where relevant DNA profiles are obtained.

To assess the viability of this alternate approach, a series of cases where digital penetration was alleged were tested by swabbing the relevant surface of the underwear prior to using the original strategy (body fluid testing/cutouts).  Samples obtained from each approach underwent DNA analysis using dual quantification (Plexor-HYTM), followed by autosomal (Identifiler PlusTM) and/or Y-STR (PowerplexY-23TM) amplification.

Nine of the eleven cases completed to date yielded positive body fluid findings (mostly in the crotch area): three with semen (via microscopic identification of spermatozoa), three with amylase results typical of saliva, and five with amylase results considered inconclusive for saliva. Swabs were collected from non-overlapping areas of the front or back panels.

Among these nine cases, male (autosomal and/or Y‑STR) DNA profiles were obtained from cut‑outs in four cases. In two of these, corresponding swabs did not yield male DNA profiles, however, additional case information indicated that the cut‑out profiles were not likely attributable to the target male. In the remaining two cases, swabs detected the same male contributor identified in the cut‑outs, along with an additional male contributor. Of the five cases in which cut‑outs did not produce male DNA profiles, swabs were successful in three cases. In one, the profile was later attributed to a prior consensual partner. In two additional cases where body fluids were not detected and cut‑outs were not collected, male DNA profiles were successfully generated from swabs.

These results indicate that swabbing, rather than body fluid testing, is an effective method for detecting relevant male DNA profiles in digital penetration cases. No probative information would have been missed using this approach, and in four cases swabbing detected male DNA not identified through cut-outs.

Authors

• Jessica Lim (Centre of Forensic Sciences, Canada)
• Sarah Johnston (Centre of Forensic Sciences, Canada)
• Ronald Lai (Centre of Forensic Sciences, Canada)
• Maria-Anna Mavros (Ontario Tech University, Canada)
• Kimberly Nugent (Ontario Tech University, Canada)
• Stacey Sainte-Marie (Ontario Tech University, Canada)
• Sonja Stadler (Centre of Forensic Sciences, Canada)
• Jonathan Millman (Centre of Forensic Sciences, Canada)