Body fluids

Semen transfer – sexual offence or innocent transfer?

Semen transfer from complainant laying on bedWhilst the presence of semen matching the DNA profile of the defendant may seem compelling evidence when it is detected on intimate swabs or clothing of the complainant, there are other mechanisms of semen transfer which might account for the findings.  A forensic sexual offences expert can consider these and evaluate the likelihood of the semen findings given the case circumstances, the allegation made and the defendant’s account.

It is often the case that when the Crown expert prepares their report, they have no knowledge of the defendant’s account and so can only comment on the findings in respect of the complainant’s version.READ MORE

Contamination – should my client be concerned?

What is contamination?

Forensic experts reserve the term contamination for transfers of trace evidence which occur after the alleged crime event or incident and are not related to the crime.  Transfer before the incident is called ‘adventitious transfer’, for example someone handling a knife whilst doing some cooking before the knife is used by another person a few hours later to stab someone.

It does not just apply to DNA, any substance of forensic interest can be a contaminant, for example body fluids, fibres, hairs, gunshot residue, paint and glass fragments.

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Use it or Lose it: Is expertise in some body fluid examinations being lost?

Yellow stain on cream fabric - Forensic body fluid analysis includes tests for urine stains As body fluid examinations have become heavily focused on the ability to obtain a DNA profile, the expertise in analysis and interpretation of tests for some of the more rarely encountered body fluids, including urine and faeces, has become limited.  Some of the main forensic providers no longer offer this testing under their UKAS Accreditation.  In a case, reviewed by Forensic Context, in which there was an allegation of the offender urinating onto the clothing of the complainant, the lack of any testing for urine was questioned by the defence and clarity sought as to whether testing was possible or simply not offered by the prosecution provider.

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When did sexual intercourse occur?

Spermatozoa viewed under a microscope (x400 magnification)

Given the nature of sexual offences, the case presented to court is often confined to one person’s word against another.  Disputed versions of events can sometimes differ in only minor ways.  In some sexual offences the timing of an act of sexual intercourse can be a crucial piece of evidence, for example if there was a consensual act with a partner prior to an alleged rape. At Forensic Context we specialise in sexual offences and our experts can provide an opinion about the time range in which sexual intercourse may have taken place, although it is never possible to say exactly when it occurred.  We can also assist with whether intercourse is more likely to have occurred at time A rather than time B.

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Washing out the stains

Clothing in a washing machine - can washing remove semen stains?

Locating semen stains on clothing usually relies initially on a chemical screening test followed by a microscopic examination for spermatozoa (sperm cells) to confirm the presence of semen. But are the tests used sensitive enough to detect semen after an item has been washed?

The term ‘washed’ can mean many different things ranging from a quick rinse, a full wash cycle in a washing machine or soaking and then washing for example.  How long the item is immersed in water, the type of detergent and temperature used will have some effect on whether semen can be detected afterwards. A scientist will need to be given as much information as possible about the type of washing used so that they can advise on the likelihood of detecting any staining and decide what tests and strategy they should employ.  This is also relevant when an expert is asked to comment on whether stains are likely to be found on a washed item, and whether the laboratory testing was appropriate. 

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