Early evidence kits in sexual assault: an observational study of spermatozoa detection in urine and other forensic specimens

To determine the detection frequency of spermatozoa in early evidence kit specimens and in subsequent full forensic specimens in alleged sexual assault.

Observational cohort study of 100 consecutive alleged sexual assault cases, presenting in Western Australia between 19th July 2008 and 6th February 2012, with both early evidence kit and full forensic evidence specimen collections. Eighty-eight cases were included in the study. Smears from all forensic specimens were analyzed by light microscopy to determine the detection frequency and structural characteristics of spermatozoa. Patient demographic features, characteristics of the alleged assault and details and timing of forensic collections were also recorded.

Spermatozoa were detected in early evidence kit specimens in 35 % (31/88) and in full forensic specimens in 42 % (37/88) of all cases (irrespective of type of alleged penetration). In alleged penile-vaginal penetration, spermatozoa were detected in early evidence kit specimens in 40 % (21/53) of cases when both first void urine and vulval gauze wipe were collected. Spermatozoa were detected in full forensic specimens in 45 % (31/69) of cases. Spermatozoa were detected in early evidence kit oral rinse specimens in 6 % (1/18) of cases of alleged penile-oral penetration and in early evidence perianal gauze wipe specimens in 33 % (2/6) cases of alleged penile-anal penetration. Spermatozoa were detected in the early evidence kit first void urine specimen in a single case, 11 % (1/9), in which the nature of the alleged assault was unknown. Spermatozoa were detected in early evidence kit specimens and not in full forensic specimens in 3 % (3/88) of cases.

Early evidence kit specimens are effective in recovery of spermatozoa, and in particular urine and vulval gauze wipe are worthwhile early forensic specimens for the detection of spermatozoa. Collection of early evidence specimens led to detection of spermatozoa-positive cases, which were not detected by subsequent full forensic specimen collection.