The end of Dlugosz style DNA evidence in court?

Last week the Forensic Science Regulator released long-awaited guidance in the area of DNA mixture interpretation. Whilst this document is still a draft for consultation and therefore not the final version, the main UK forensic providers have all had input and therefore changes are likely to be minimal.


Of particular note to legal professionals are the following guidelines:

Guideline 16

The practice of offering a qualitative evaluation in a case where, because of unresolved interpretative issues, it has not been possible to carry out a quantitative evaluation by means of validated software, should not be continued.

The introduction of sophisticated software packages means that some complex mixed DNA profiling results can now be statistically evaluated.  However, there are still limitations with regards to the type of result that the software can handle. In the situation where a statistical evaluation has not been possible, but the profile of the person of interest is fully represented within the DNA profiling result, some experts have provided an opinion with regards the evidential significance. Following the Dlugosz judgment in 2013 there has been much debate regarding whether these ‘qualitative evaluations’, relying only on the expert’s experience, should be used. You may have encountered such a situation – when no statistical evaluation has been possible and the expert states, for example “there is at least strong support for the view that the defendant contributed to the DNA mixture, rather than he did not”. Cellmark Forensic Services have stood alone in providing these evaluations for evidential purposes, whereas LGC Forensics have provided such an evaluation for intelligence purposes only (guideline 15 still permits the latter approach). We have argued in many cases that the use of a qualitative evaluation was unsupported and potentially misleading with regards to the evidential significance of the findings. In some cases, the judge dismissed DNA evidence where only a qualitative evaluation could be given, but in others the evidence was put before the court.

This proposed guideline now makes it clear that qualitative evaluations for evidential purposes should not be continued, although guideline 15 allows for the continued use of such opinions for intelligence purposes to assist an inquiry.

Guideline 17

The practice of including prosecution-aligned expressions of possibility in statements should be discontinued

In statements provided by the Crown, we often see an interpretation along the line of the defendant ‘could have been a contributor’ to a mixed DNA profile. Whilst there is usually no dispute with this, it is an unbalanced view and fails to point out that the defendant also might not have been a contributor. Where a statistical evaluation is provided, this of course provides a weight for the view that the defendant has contributed rather than the view that he had not. But where a statistical evaluation is absent, such expressions of possibility are not informative and risk the court applying a greater significance to the findings than they merit.

There is much more information within the guidelines. We would be very happy to assist if you have any questions regarding how the guidelines relate to the DNA findings in a specific case, or if you would like to arrange a CPD presentation.