Knox/Sollecito DNA showdown: an overview (part one)

This Monday, 25th July, will be the most significant date so far in the appeal of Amanda Knox and Raffaele Sollecito against their 2009 conviction for the murder of Meredith Kercher. The court in Perugia will begin hearing arguments about two pieces of disputed DNA evidence on which doubt has recently been cast by a review. These arguments are likely to stretch over a number of hearings and travel into the intimate details of DNA analysis and the investigative process in the case. It would be misleading to suggest that we will know the outcome of the appeal just on the basis of this group of hearings. On the other hand, more will rest on the relative strengths of the defence and prosecution arguments in respect of these two pieces of evidence than on anything else that has been, or will be, discussed in court during the appeal process.

The DNA review in a nutshell

Stefano Conti and Carla Vecchiotti of the Sapienza University of Rome were asked by the court to review DNA evidence relating to a knife, allegedly used by Knox to stab Kercher, and the clasp of a bra removed from Kercher’s body after she was attacked.

On the basis of a number of factors, Conti and Vecchiotti take the view that the amount of Kercher’s DNA found in the sample taken from the blade of the knife is so low that it should be classified within a bracket known as Low Copy Number (LCN). This being the case, particularly rigorous procedures should have been applied in the handling of the knife by investigators and during the laboratory analysis of the DNA sample. Conti and Vecchiotti take the view that procedures at the crime scene did not meet these standards. They say they are not able to comment on the general standards in the laboratory, but they note that a number of measures that could have been taken to provide reassurance about the possibility of lab contamination were not.

They looked at two DNA printouts relating to the bra-clasp, one reporting the autosomal DNA of the sample taken from it (i.e. a standard DNA matching test) and one reporting details about the makeup of the y-chromosome content of the DNA. In both of these printouts, they identify peaks alongside those relating to Sollecito and Kercher which, although dismissed in the original testing as noise, they feel ought to be treated as genuine alleles, that is, as representative of real DNA information in the sample. There are a number of possible explanations for the presence of such additional DNA, but the authors of the review suggest that the possibility that these are evidence of low-level contamination of the sample cannot be ruled out. And, if contamination of the sample cannot be ruled out in general, then contamination of the sample with the DNA of Raffaele Sollecito also cannot be ruled out.

Clearly, these findings are good news for the defence. But the big question is how they well they will withstand scrutiny in the courtroom.

In my estimation, at the time the legal teams begin their arguments, the cards will be stacked in favour of the defence with respect to the knife. Specifically in relation to the question of contamination in the lab, the logic of the review is compelling, as I outlined in this post. If the knife is to be kept in play as evidence, then the onus surely falls on the prosecution the show that the risk of contamination was substantially mitigated by the strength of the procedures in place during laboratory analysis.

In contrast, I think the prosecution will walk into the courtroom with the upper hand as far as the bra-clasp is concerned. The court may be impressed by what Conti and Vecchiotti have to say to the extent that it will agree that contamination ought to be taken seriously as a possibility. But, in order to disregard the bra-clasp as evidence, the theoretical possibility of contamination may not be enough. The court will also need to be persuaded that contamination should be seen as plausible in practice, given the facts of the matter. And, in this respect, the review is weaker, appearing to offer only hypothetical and, arguably, not particularly likely-sounding accounts of how it might have taken place. So, a key task for the defence will be to try to paint a more vivid picture of this for the court.

That’s my view. But there are no foregone conclusions here. What I think it might be possible to discern, though, is the nature of the questions that the court will need to get answers to in order to come to a conclusion about these two troublesome pieces of evidence.

Coming up in the next post: key questions for the court


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