News & Views

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

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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The end of Dlugosz style DNA evidence in court?

Last week the Forensic Science Regulator released long-awaited guidance in the area of DNA mixture interpretation. Whilst this document is still a draft for consultation and therefore not the final version, the main UK forensic providers have all had input and therefore changes are likely to be minimal.

 

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Can we rely on the DNA match statistic from Specialist Statistical Software?

DNA Mixture software

As DNA profiling methods have become ever more sensitive, the detection of trace amounts of DNA has improved. Hence the number of DNA mixtures we encounter has increased.  This was especially highlighted following the introduction of DNA17 methods in 2014. In many situations the mixtures have multiple contributors and are complex to interpret.  Whilst previously many results were designated as too complex for interpretation, the last couple of years have seen the introduction of ‘probabilistic genotyping software’ packages which enable a statistical evaluation of complex results.

 

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When did sexual intercourse occur?

Spermatozoa (x400)

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

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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DNA transfer through non-intimate contact

Male and Female symbols

In sexual offence cases where no semen is detected, the presence of female DNA on penile swabs and underwear of the defendant may be put forward to address the issue of whether or not sexual intercourse took place.  However it is known that DNA can be transferred through non-intimate contact so research was commissioned to investigate the frequency and amount of DNA which might be transferred in this way.  The work was recently published in Science and Justice by the UK and Ireland Association of Forensic Science Providers’ Body Fluid Forum which our expert Julie Allard co-chaired at the time of the research.
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