Body Fluids - Semen and Vaginal Material - Forensic Science For Sexual Assaults and Rapes

Following an allegation of sexual assault or rape, it is most likely that a victim will be examined by an experienced medical examiner. During this examination, intimate swabs will be taken for detailed forensic examination. Hair combings may be taken and fingernails scraped in case the suspect, during the assault scratched the assailant and traces of skin, etc. were transferred. The clothing of the victim will also be taken for detailed examination (for body fluids, DNA, hairs, fibres, etc.).

During a sexual assault or rape (man to woman) the semen of the assailant may or may not be transferred whether or not sexual penetration took place. During the forensic investigation of an alleged incident, the forensic scientist will examine (chemically and microscopically) the intimate swabs and clothing of the victim for traces of semen. Semen is not always detected, for example, the assailant may have used a condom, ejaculation may not have occurred or the donor may have had a vasectomy or have a low sperm count. (If a condom was used the victim's swabs can be anlaysed for the prescence of condom lubricants).

If ejaculation did occur the detection of semen is dependent on several other factors such as if the victim has bathed since the alleged incident or if there has been a time lapse before the medical examination.

Vaginal material may also be transferred during sexual intercourse. Vaginal material contains epithelial cells from the vaginal wall which appear microscopically similar to the cells present in an ejaculate of semen.  In cases of alleged sexual intercourse, DNA profiling may help if a mixture is obtained from a penile swab taken from the suspect and our scientists are highly trained in the interpretation of complex mixtures.

Other bodily secretions such as urine and faeces can also yeild forensic evidence, and may have been searched for and analysed by the prosecution.

As can be seen the forensic science used in cases of sexual assault and rape can be complex and detailed with many different scientific techniques used. Some of these techniques, such as DNA profiling, are extremely sensitive, and, potentially, open to contamination. Of course, finding the body fluids is one thing, interpreting from whom they came and how they got there can be very complex.

There may, in more violent attacks, be blood present, which can be subject to blood pattern analysis (BPA). Other evidence types such as the examination of exhibits for textile fibre transfer, may also be involved in cases of rape and sexual assault.

Our forensic scientists have extensive experience in dealing with these complex cases of sexual assault and rape from the defence and prosecution point of view and can use this expertise to examine a case in detail. For example, we can:

• re-examine exhibits previously examined by the prosecution, looking for body fluids not previously found and to ensure that there has been no other evidence type missed. There may be traces of DNA from other persons, other than the accused, that has not been found previously;
  
  
• examine the types of body fluids found, and where they were found and the interpretations made by the prosecution and test the hypotheses produced. Is there an alternative and realistic scenario of how these body fluids were transferred?
  
  
• check that the procedure used to examine and search the exhibits and any subsequent DNA profiling were in compliance with the laboratory’s stated, quality management procedures;
  
  
• check to see if their has been any chance of contamination of the items. DNA profiling and the detection of semen and vaginal material are very sensitive techniques;
  
  
• discuss the interpretation of the results with the prosecution scientist, exploring weaknesses and strengths of the interpretation;
  
  
• check and assess the credibility of the prosecution's forensic biologist and DNA profilers;
  
  
• look for and explore realistic and viable alternatives to the interpretation of evidence and the translation of that into how/when the event occurred and how any detected body fluids were produced;
  
  
• produce a detailed report of the findings including photographs and diagrams where appropriate.

At Forensic Access we are proud of our forensic scientists, with some of the leading forensic biologists in the UK working for us. See our list of experienced forensic scientists.

Contact Forensic Access to see how we can assist you with your case work.