Body Fluids

The presence of blood, semen, saliva or vaginal secretions is often significant across a range of case types, predominantly sexual offences, murder, violent crimes, robbery, burglary, possession of drugs and firearms.   As well as the body fluids named above, cellular material deposited by touch or contact has also become increasingly important given the high sensitivity of current DNA profiling methods which are key in identifying from whom biological materials may have originated. Urine and faeces are rarely encountered as a relevant evidence type, and establishing the possible source of these by DNA profiling is often difficult

When our experts undertake defence work to review cases, they will  scrutinise the reliability of the tests used to identify staining as a particular body fluid, assess the amounts present and consider whether the distribution or pattern of staining is significant.

Our experts were involved in the development and validation of many of the methods used today so have intimate and extensive knowledge of the strengths and weaknesses of the techniques used.

Identification of body fluids

During our reviews of other experts’ findings, we rarely encounter  issues with the location and identification of stains such as blood and semen, as straightforward standard tests are employed.  The identification of saliva can be more problematic and open to differences in opinion, especially when it is mixed with other body fluids and there is currently no routine test to identify vaginal secretions.

Distribution of staining

In our experience  it is usually the distribution and amounts of staining that are relevant when evaluating forensic findings against the accounts of the complainant and defendant; for example

  • Is the staining on the inside or outside of a garment?
  • Is there a small trace or a large amount present?
  • Could the body fluid and DNA have been transferred as a result of direct contact or deposition, or might it be due to an indirect transfer via an intermediary (secondary, tertiary transfer etc)?
  • What might be expected given the prosecution account versus the defence account?

Dried stains of body fluids or cells will remain on an item until it is thoroughly washed, wiped or lost due to other contacts. It is not possible to determine the age of a stain other than to say it was deposited since the item was last thoroughly washed.

Blood pattern analysis (BPA)

Violent crimes can often result in bloodshed which gives rise to bloodstaining with distinctive patterns being deposited on surfaces at the crime scene, on any weapons and on the clothing of the people present. When examined by a blood pattern expert, the appearance and distribution of the bloodstaining can yield valuable information concerning the events which lead to their creation.  Blood patterns generally have much more distinctive visible patterns than other body fluids. Our experts will undertake a detailed examination of the nature, extent and pattern of bloodstaining to assist with  evaluating the findings against the accounts of  the injured person, the accused and any witnesses.

Has the DNA originated from a specific body fluid?

There can be differences in experts’ opinions as to whether the DNA profile obtained from an area of staining can be ‘attributed’ to a specific body fluid related to the alleged crime, or if it is for example from underlying DNA that may be present as result of legitimate actions. It is important that an expert’s report is explicit about their opinion on the attribution, or not, of the DNA to a specific body fluid.

Absence of a body fluid

In some cases, an absence of staining can be significant. However evaluations in respect of this are much more difficult, especially when there is limited information about the alleged actions that took place.  The expert will need to consider whether any body fluid deposited during the alleged incident could have been lost due to degradation or loss over time, particularly with intimate swabs taken for sexual offence investigations. Bathing or washing may completely remove or reduce the amount of a body fluid deposited on skin or in body orifices. Washing of clothes may also have the same effect.

In some cases the absence of staining will be probative. Consider for example  a case where a man has been beaten and there is a high expectation of a transfer of blood to the assailant given the nature of the alleged assault and the injuries.  An absence of blood on the defendant’s clothing would favour a defence account of no involvement, assuming that the defendant had not changed or washed his clothing.

If you would like advice about any aspect of body fluids or DNA, contact us and speak to one of our experts.