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.

 

 

You may see the Crown expert use phrases such as:

  • The scientific findings support the allegation that intercourse occurred.
  • The findings could explained if some form of sexual activity occurred.
  • The scientific findings are as might be expected if the incident occurred as alleged.

However such ‘conclusions’ could be considered to be prosecution biased and if put to the court may result in a misunderstanding of the evidential weight of the findings. It is crucial that the scientific findings are evaluated by an expert in relation to the accounts of both parties and that a balanced conclusion is provided to assist the court as to whether the findings favour one account over the other.

How is semen transferred?

Semen can be transferred by direct or primary transfer, for example by ejaculation directly onto a bed sheet or into the vagina during sexual intercourse. Drainage of semen from the vagina after intercourse can result in semen staining on lower clothing and bedding depending on the circumstances following the alleged intercourse.

Indirect or secondary transfers of semen can also occur in which the transfer is via an intermediary. For example, a child wearing a clean nightdress sits on a semen stain present on the bed sheet and semen is transferred to her nightdress.

The amount of semen that is transferred by indirect transfer is generally less than that which would be transferred by direct means, however it also depends on whether the staining is wet or dry, and the amount of contact between the surfaces.  In this example, if the semen stains on the bed sheet had been dry, the likelihood of semen transferring to the nightdress is lower than if the staining had been wet. A transfer from dry staining is likely to be in smaller amounts compared to a transfer from wet staining.

In theory, transfer can occur via more than one intermediary i.e. tertiary, quaternary transfer etc., but as the amounts will diminish with each transfer it is rarely detected.

In general, where strong semen stains are found they are most likely to be the result of a direct transfer. When small amounts of semen are found, the possibility of indirect or secondary transfer has to be considered.

It might also be important to consider whether it is possible to determine whether the semen detected was transferred to the inside or outside of an item of clothing.  Whilst scientist’s reports often indicate which surfaces have been tested, the detail is often missing regarding whether it is possible to say on which surface the semen was deposited.

Some case examples where consideration of indirect transfer of semen is important 

An allegation of intercourse where the defendant says only digital penetration occurred

Small amounts of semen were found on the complainant’s vaginal swab. Our expert considered whether this was more likely to have been deposited directly during the alleged sexual intercourse rather than having been transferred by the insertion of a semen stained finger into the vagina, as alleged by the defendant. This entailed consideration of the time since the alleged incident, the actions of each individual and the amount of semen detected.

An allegation that a family member had intercourse with a child

The child’s underwear was found to be stained with a very small amount of semen. Our expert reviewed the Crown’s findings and concluded that that they were inconclusive in respect of addressing the issue of intercourse.  Her opinion was whilst the findings could be explained by sexual intercourse,  the semen could have been deposited as a result of the underwear being in contact with another item within the household which was stained with the defendant’s semen. This included the possibility of a transfer of semen having occurred from semen stained bedding when the child had slept in the defendant’s bed, when the child’s clothing had been in a laundry basket with items stained with the defendant’s semen or from a transfer occurring when such items were washed together.

Semen on the complainant’s trousers which the defendant says was transferred from wet semen on his clothing

It was alleged that some form of sexual activity had taken place between an underage girl and the defendant, although both parties denied this. The defendant said that wet semen must have transferred to her trousers from his clothing when she had sat on his lap. Whilst there was some semen staining on the complainant’s trousers, it was not possible to determine whether this staining had originated from the inside or outside surface of the trousers. Our expert considered that the findings were within the range of expectations for semen transfer if the defendant’s account were true. Overall she concluded that the findings were inconclusive with regards to distinguishing between the allegation and the defendant’s account.

 

The evaluation of the likelihood of a stain arising as a result of an indirect transfer can be complex. The expert will need to consider the amount and location of any semen staining and the DNA results in the context of the case circumstances and the accounts given by the complainant and defendant.

Forensic Context’s experts have a high level of specialist forensic knowledge and expertise in the evaluation of semen transfer in sexual offence cases. Please phone or email us and we can provide you with early advice.