Forensic DNA profiling has been described as the ‘Gold Standard’ of forensic disciplines. That standard was perceived by many to have dropped considerably in the UK when the Court of Criminal Appeal delivered the judgement in the case of Dlugosz.
“As we have said, evaluative evidence is admissible provided that the judge is satisfied that the expert giving that evidence has a proper basis for giving the evaluative evidence based upon his or her experience and the features of the mixed profile enable this to be done.”
The unfortunate fact, not apparently appreciated by this Court (and some others), is that,
“there is no scientific basis for this belief - no scientific literature provides a reliable methodology, scientists are not trained to make such assessments and there is no body of standards to support them. Casework experience is not a substitute.
The true composition of the DNA result in any given case cannot be known so it does not provide a reliable control for learning purposes.”[1]
Despite the Dlugosz judgement, we have challenged the DNA evidence in several cases in which we have been involved since Dlugosz where the prosecution presented the weight of the DNA evidence with either a subjective evaluative opinion or no evaluation at all. In the last week, three trials in London, Belfast and Liverpool in which we were involved have seen the Crown withdraw such evidence.
Of course, one may argue that is all well and good; bad science should not be put before the jury. However, there is another view that perhaps by withdrawing the evidence the Crown ‘live to fight another day’ having had no adverse judgement against them. One judge indicated that he would have ruled the evidence inadmissible had the Crown not withdrawn it. Are the challenges being made or are others simply accepting Dlugosz?
We have already commented on Dlugosz and on using experience as the basis of scientific opinion. It appears that regardless of Dlugosz, viable challenges exist to forensic DNA profiles that are not supported by robust statistical calculations.