DNA profiling can provide apparently very powerful evidence when a profile matching an individual is found on an item or a person associated with a crime. However given the very high sensitivity of current methods in detecting minute traces of DNA (from just a few cells), it is crucial that an evaluation is undertaken by an expert regarding how and when it may been deposited.
It is important for an expert to consider the following aspects alongside whether the DNA match itself can be relied upon:
- Is the DNA attributable to a specific body fluid, such as semen, blood, saliva?
- Is the presence of a body fluid from an individual significant in the context of the case information whereas the presence of their DNA (not attributable to a specific body fluid) may have an ‘innocent’ explanation?
- Could the DNA or body fluid be the result of an indirect transfer (secondary, tertiary etc) or is it more likely to have been deposited due to direct contact with the relevant surface?
- Where was the sample taken from, is its location significant?