Knox/Sollecito DNA battle – who won?

Prosecution advisor Giuliano Mignini and defence expert Carlo Torre in court today. Picture from Umbria24.it

As courtroom debates over DNA draw to a close, tweets and early reports from English language journalists in Perugia covey a mood that things are going in the defence’s favour in the appeal of Amanda Knox and Raffaele Sollecito against their convictions for the 2007 murder of British student Meredith Kercher.

Maybe there’s some basis for this, but I’m unconvinced. One possible reason for taking such a view might be a misreading of the thing that’s hogged the limelight in reporting over the last 48 hours. Yesterday, prosecution expert Giuseppe Novelli criticised Carla Vecchiotti and Stefano Conti, the scientists who conducted a review of DNA evidence, for their decision not conduct a full re-test with regard to the kitchen knife alleged to have been used in the murder. According to Novelli, this could have and should have been done. It was an inexplicably missed chance to confirm the validity of the original testing.

Today in court, the prosecution formally requested further testing of the knife, but the request was declined. My impression is that some have taken this as a significant clue as to the thinking of presiding judge Claudio Pratillo Hellmann. But I don’t think it is. Whatever is between his ears, he was never going to accede to the request. Knox’s lawyer Luciano Ghirga objected in court that holding a second review of DNA evidence is virtually unheard of, and I don’t doubt that this is correct.

And re-testing wouldn’t have had much value in any case. If it had failed to find the DNA, that would not have excluded the possibility that there was DNA there at some point. And if it had found the DNA, that would not have excluded the possibility that it got there by contamination, as the defence have argued. The prosecution were sensible not to miss an opportunity to demonstrate with intent how confident they are about the validity of the evidence, safe in the knowledge that their bluff was never going to be called. But the inevitable rebuff means nothing.

It’s not easy to predict what the bench will end up making of the DNA evidence overall. That’s partly because the answers they are looking for are in the boring technical detail gone over by the experts in court, much of it obscure and most of it unreported. But, with regard to the knife, assuming they follow the explanations of the science they have heard in court, I don’t think the judges have much option but to accept that it is valid evidence.

Six weeks ago, it was another story. The possibility that the knife was contaminated was the ace in the defence’s hand. The DNA review said it was possible and it was not easy to see how any reasonable scientist could disagree. The quantity of Kercher’s DNA found was tiny and, unless everything was done extremely carefully, a tiny amount of DNA in a test can be the result of contamination.

There was never a real chance that this contamination could have occurred during the recovery of the knife, because this had happened at Sollecito’s flat, where Kercher had never been, and there is no good reason to think that her DNA might have been there. But the DNA review reported a lack of detailed information about how tests were conducted in the lab. So, unless the prosecution were able meet the burden of showing that everything in the lab was hunky dory, prudence dictated that the possibility of contamination there could not be ruled out.

That picture flipped in testimony on 30th July, when one of the authors of the DNA review, Carla Vecchiotti, was asked about the difference it might make if it could be shown that no material relating to the Kercher case had been tested in the lab during the six days prior to the testing of the knife. That could rule out the possibility of any of Kercher’s DNA being present in the lab in order to contaminate the knife. Vecchiotti said that six days was long enough for this to be the case. Perhaps tellingly, the defence don’t seem to have put forward any counter-argument to this.

Which means that the defence case with regard to the knife is effectively reduced to the proposition that the DNA sample was too small and some of the peaks in the printouts were below 50 RFU in height. It is what is sometimes referred to as “low copy number” DNA. But the argument is weak without the possibility of explaining a consequent risk. There’s no doubt that the sample is a match to Kercher and if there’s no possibility of contamination, who cares how small the sample was? And why should they? This line of defence seems to amount a plea to turn back the scientific clock. As DNA analysis has improved, it has become routine around the world (with the notable exception, until recently, of the US) for convictions to be based on tiny quantities of DNA. It happened in the Anna Lindh case, the Peter Falconio case and, in the UK, over 500 cold cases have been reopened using low copy number DNA evidence. The judges in the Kercher case ought really to treat the idea that the sample is too small in the same way they would treat a plea for a speeding ticket to be thrown out because it was printed in 6-point font.

Arguments regarding the clasp from Kercher’s bra, said to have had Sollecito’s DNA on it, appear slightly more finely balanced. The same principle as in the case of the knife would appear to rule out the possibility of contamination in the lab. But the judges fact a genuine dilemma when they consider the possibility of contamination at the scene of the crime. The prosecution point out that Sollecito’s DNA was only found in one other place in the flat, so it’s not as if the place was swimming in it. And there’s no real reason for it to be found in Kercher’s bedroom, which is where the clasp was recovered from.

But, whilst it may be true that the chances are not high, the question for the judges is how high do they need to be? That’s very subjective. They’ve been played a DVD showing various alleged breaches of protocol by investigators in handling evidence, such as failing to wear the right protective clothing and putting some of the evidence into plastic bags rather than paper ones. They also have to consider that the clasp moved across the floor of the bedroom between its discovery and its eventual bagging over a month later, by some means that has not been accounted for. These things don’t necessarily carry with them a huge increase to the risk of contamination. But the judges might just feel that the risk doesn’t need to be huge to be significant.

It also has to be acknowledged that, whereas there remains a considerable amount of evidence against Knox with or without the knife, the clasp is a fairly big part of the case against Sollecito. I don’t think he’s likely to walk free, but maybe it isn’t unimaginable.

And it seems that lead prosecutor Manuela Comodi has enough imagination to conceive of the possibility that the case may not go her way. On the one hand, this only seems like stating the obvious. But something seems wrong with any picture than involves a lawyer being candid with journalists.

Closing arguments begin on 23rd September.