semen Tag

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

Has the defendant’s DNA come from semen?

 

Microscopic preparation from a vaginal swab stained with semen (400x magnification)

 

The Crown’s forensic report states that semen has been detected and that a DNA profile matching your client has been found.

 

You might assume that the DNA came from the semen.
But that may not always be correct!

 

The reason is that the DNA could originate from another body fluid or cells present in the same area as the semen and therefore any attribution of the DNA profile to the semen present may not be robust.

Semen consists of a fluid (seminal fluid) which contains spermatozoa (sperm cells). Although the DNA profiling process usually includes a step that preferentially extracts DNA from the sperm rather than from any other cells, this is not always 100% effective. In other cases, because the amounts of semen are so low, this preferential extraction step is not used.

 

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Forensic Medical Examination Standards

latex gloves worn to minimise contamination during a forensic medical examination

Two very pertinent documents regarding standards for forensic medical examination in cases of alleged sexual assault in England and Wales were published on 27 May 2020 by the Forensic Science Regulator (FSR).    These were developed  by our expert Julie Allard  and other experts from Principal Forensic Services (PFS), in conjunction with experts from Lime Culture CIC and the FSR’s Medical Forensics Specialist Group.The standards underwent public consultation prior to final publication in May 2020.

Examination Standards

FSR-C-116 Sexual Assault Examination: Requirements for the Assessment, Collection and Recording of Forensic Science Related Evidence
FSR-G-212 Guidance for the Assessment, Collection and Recording of Forensic Science Related Evidence in Sexual Assault Examinations

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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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