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The future of DNA profiling – how will it affect your cases?

Duncan Woods

By Duncan Woods on 22/05/15

The future of DNA profiling – how will it affect your cases?

You may be unaware that a major increase in the sensitivity of DNA profiling techniques used in the UK is being introduced. At a scientific level, this marks the latest improvement in profiling technology, but when it comes to assessing the evidential value of the results, much of the knowledge accumulated over many years’ use of the old technology will become less certain.

On one level, the new methods will obtain detailed profiles from the type of samples that previously would have failed or produced results that could not be said to be significant. Samples that previously gave low level, uninterpretable results may now give interpretable results. The improvements are such that we are sure many old, cold, unsolved cases are likely to be revisited. Old stored samples and exhibits will be recovered and analysed to see whether valuable results can now be obtained.

There is, however, a down-side to this development: these methods have an increased tendency to produce mixed profiles from many types of samples, because they will detect not only the DNA in a stain or skin debris, but also any underlying DNA present from other sources. All the DNA and cellular debris that transfers during normal daily life between people’s clothing and skin, particularly in domestic circumstances, will now have a much greater tendency to be detected in the profile results. This means that the very significant issue of attribution uncertainty is increased. That is, if you obtain a mixed profile from a faint saliva or blood stain, or from a tiny blood spot or loose surface debris recovered on adhesive tape, how do you know which of the people represented in the mixed profile provided the blood or saliva or skin debris? Uncertainty in the attribution of individual profiles to specific types of body fluid can have a very significant effect on a wide range of criminal cases.

To complicate matters, the current forensic service providers are each opting for one or more of the new analytical systems, so there will no longer be one universal system for the UK. Also being introduced are a number of highly sophisticated statistical methods for drawing out significance from complex DNA profiles which previously would have been given little or no evidential value. In other words, from the sort of multi-person, mixed DNA profiles that a frequency figure could not be attached to. These software packages will provide a much more powerful tool when it comes to trying to identify whether the DNA of a particular person, defendant or victim, is represented within a complex mixed profile, however, they will not assist with the question of correct attribution or in determining the significance of the results vis-à-vis an alleged action over a defence alternative.

Both the new methods of producing DNA profiles and the new statistical methods have arrived at about the same time, compounding the advantages and disadvantages. They are being implemented now throughout the UK, and are being used in investigations. This has implications on forensic experts such as us to be ahead of these developments and their consequences in case work, and to understand which techniques are being employed by which of the prosecution forensic laboratories, when they are being implemented and how well they have been validated.

It is also important that there is raised awareness amongst those responsible for advising defendants and preparing cases for court, that their previous knowledge may no longer apply and some of the old convenient assumptions may no longer be correct. Ideally this should exist from the interview stage, to ensure that the forensic results are not misrepresented in questioning, right through, if necessary, to testimony at court. Otherwise we risk an increase in the number of occasions in which courts process criminal cases without accurately understanding the evidential value of the forensic results that form part of the prosecution.