Information from penile swabs in sexual assault cases

Abstract

A survey has been made to assess the evidential value of tests carried out on 660 casework penile swabs. Most were from suspects in sexual assaults and were examined to see if the donor had had recent anal, oral or vaginal intercourse. The swabs were tested for one or more of the following: blood, faeces, saliva, vaginal secretions, semen. Blood was seldom found, it was usually weak and insufficient for grouping. Faeces were only identified on a pair of swabs from a dead homosexual showing that proof of buggery by this means is rare. Amylase, suggestive of saliva and oral intercourse, was occasionally detected. Glycogen-rich epithelial cells were sometimes present indicating vaginal intercourse. Semen was frequently found but its presence may not result from a recent sexual act. An ABO group different from the donor was obtained from a fifth of the swabs typed. Grouping in other blood group systems was rarely attempted or successful. Penile swabs provided a means of detecting a victim's ABO blood group on a suspect when it would not have been possible to demonstrate the suspect's group on samples from the victim. They also had value in assaults involving more than one offender. The main limitation of penile swabs was the paucity of material on them and the sampling site affected the interpretation of the results.