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

This is a continuation of the previous post.

Questions for the court

1. How certain are Conti and Vecchiotti of their conclusions?

Francesco Maresca, lawyer for the Kercher family, has made clear his view that the DNA review is simply too unequivocal. Whereas it might have weighed up various differing viewpoints and given indications of the relative strengths of different arguments, it is instead content to give a rather bald and linear opinion. Prosecutors will undoubtedly be hoping that greater acknowledgement of the complexities of DNA analysis can be extracted from Conti and Vecchiotti during questioning.

It may be a struggle to get them to cast doubt on the central threads of their own arguments. But maybe they will be willing to give way to the prosecution case on certain details. For example, one thing they suggest is that the bra-clasp might have become contaminated with Sollecito’s DNA because it hitched a ride on air-born dust. It might be felt that it would not be too big a deal for them to agree that this is, in reality, just as speculative as it sounds.

Getting concessions on those sorts of apparently minor details could do a lot to aid the prosecution case in two ways. Firstly, the logic contained in the DNA review might thereby be eroded. What’s more, from a tactical point of view, it can’t hurt to have its authors agreeing that there is more to what they say than meets the eye, even if that is something that can only be achieved on the fringes.

2. How clean was the lab?

If the prosecution can’t bring a convincing argument that the procedural standards in the laboratory where the DNA tests were carried out, then it may be that the court will lose confidence in the proposition that the knife can be considered to have been used in the crime.

The lab was preparing for ISO 9001 accreditation at the time when the tests were carried out. This may be significant, because that process included the development of internal process auditing. In other words, it may be that an audit report exists which will give a description of how analytical tasks were carried out in the lab at around that time. If so, then that document may well be able to tell the court everything it needs to know in order to determine the reliability of the testing carried out on the knife blade.

Whether such a report exists in reality and whether it will be entered as evidence is, of course, unknown.

What is also unknown is where things stand if, as may well turn out to be the case, the court has only the word of police scientist Patrizia Stefanoni or other people connected to the lab. Is it then just a question of the court’s credulity?

3. Where are the controls?

Conti and Vecchiotti say they can find no evidence that appropriate control experiments were run in tandem with the DNA testing on the knife so as to help ensure its reliability. In particular a negative control (i.e. running a “blank” test and checking that the results turned out blank) could have provided some evidence against the possibility of contamination.

If such controls were not carried out, is there any way in which this is defensible? If controls were carried out and were satisfactory but not recorded, is that good enough?

4. When is a stutter not one?

The DNA review employs simple but strict and inflexible mathematics in order to make distinctions between peaks in DNA printouts which should be considered stutters (meaningless noise) and those which should be considered genuine parts of the DNA information produced. For each peak, there is a height threshold, above which it should be considered genuine and below which it should not. It is on this basis that they identify evidence of “spare” DNA on the bra-clasp, which may be attributable to contamination.

But do things have to be as strict as they make out? Conti and Vecchiotti give the impression that their approach is generally accepted among DNA analysts. If that’s the case, though, why did the defence experts in the original trial not follow the same line of reasoning?

5. Can the “spare” DNA be accounted for?

It seems an obvious question to ask. If there is additional unexplained DNA on the bra-clasp, can it be associated with any particular individual? There isn’t enough DNA to make a definitive match to anyone, but a fairly good indicative match might be possible. The prosecution would score an enormous point if they are able to tell the court that the additional peaks on the graph are compatible with, say, Kercher’s Italian boyfriend or Knox and Sollecito’s alleged accomplice Rudy Guede. That would mean that the mystery DNA is not evidence of contamination after all, and so the rug would be pulled from under the logic set out in the DNA review.

On the other hand, if it were to emerge that the DNA is compatible with someone from the police’s investigative team (assuming, in the first place, that it is permissible to check from a Human Rights point-of-view), then that would make the contamination thesis seem all the more probable.

  • UPDATE: Since posting, I’ve been able to check the “spare” DNA against Rudy Guede’s profile. There does not appear to be any clear match.

6. How likely is crime scene contamination?

Even if the court is persuaded that contamination – either of the knife, the bra-clasp or both – at the crime scene or in subsequent handing is a possibility to be taken seriously, they may form the view that there were, in reality, no realistic opportunities for such contamination to take place.

The knife was found in a location – Sollecito’s apartment – where Kercher had never been, and so it may seem difficult to imagine how it could have come into contact with her DNA (at least, that is, prior to its arrival at the laboratory, where various samples relating to Kercher had already been tested). The bra-clasp spent a number of weeks lying on the floor in Kercher’s room before it was recovered, so there’s a big window of opportunity for contamination to have taken place. But, again, its not clear how Sollecito’s DNA in particular might have found its way onto the clasp. The amount of his DNA found there is quite large (in fact, it might be argued that this in itself tells against the possibility of contamination), but there does not seem to be good reason to suppose that large quantities of Sollecito’s DNA might have been present in Kercher’s room – a least, not without placing him there at the time she was attacked.

An important job for the prosecution, then, will be to try to convince the court that, from a scientific standpoint, that’s a mistaken way of seeing things. So, they are likely to spend time talking about research suggesting that contamination can be found even in the circumstances in which you would least expect it, and they’ll be hoping that Conti and Vecchiotti and willing to back them up in this regard.

But they will need to strike a fine balance. They need to make the point forcefully, but without appearing to over-egg the pudding.

7. Could DNA be present due to secondary transfer?

“Secondary transfer” is a term used to describe the process of someone transferring someone else’s DNA to a given location. The defence may wish to make the suggestion that this could have happened in either of the cases we are talking about. Either Knox or Sollecito could have had a tiny amount of Kercher’s DNA on their fingertips, for entirely innocent reasons. Either he or she then touched the knife, and the rest is history. Equally, if Kercher had a tiny piece of Sollecito’s DNA on her fingers, it is not hard to see that she might have transferred this herself to her bra.

With respect to the knife, there’s a commonsense reason to be sceptical. Secondary transfers from Kercher were not found elsewhere in Sollecito’s apartment, and it would seem like one hell of an unlucky coincidence if the one place that it had happened was the blade of a knife. But there’s also a scientific reason for scepticism. Research has shown that making a secondary transfer without also transferring large quantities of your own DNA is extremely unlikely. So, if either Knox or Sollecito had transferred Kercher’s DNA to the knife, we would expect to find their DNA mixed into the sample. But it is not there.

The bra-clasp sample, on the other hand, is more compatible with secondary transfer, in that DNA from both the supposed transferor (Kercher) and the supposed transferee (Sollecito) are present. But the problem for the defence in this case is the circumstantial information we have about the sample. We know that someone removed Kercher’s bra after she was attacked. And so, it would seem sensible to suppose that it is at least possible that that person’s DNA might be on her bra-clasp. And what do we find on the clasp..? Bingo! Or so one might think. A key question for the court here is whether the mere possibility of an alternative explanation – let’s face it, there will always be such possibilities – is enough for them to set aside the evidence.

8. What if both of these items of evidence cannot be relied upon?

If the court feels that both the bra-clasp evidence and the knife evidence are unreliable, then the question at the back of their minds will be whether enough evidence remains to uphold the convictions of Knox and Sollecito.

If the report of the assize court is anything to go by, then there quite plainly is. But the appeal court is not necessarily obliged to agree with the lower court on every point. For the defence, it is probably a vain hope that a different conclusion will be reached on every single item of the prosecution case. But how much evidence will be enough?

Most of this evidence isn’t due to get discussed again in court. It will, instead, be discussed by the judges and juror-judges in private. So, whatever happens over the next few sessions, it may be that there is no real indication of what the verdict will be until the moment it is announced.

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6 Responses to Knox/Sollecito DNA showdown: an overview (part two)

  1. cjp says:

    Maundy, do you know if the lab was seeking it’s initial ISO accreditation, or was it already certified and getting ready for audit?
    The distinction is important, in my opinion.

    • maundy says:

      The lab got its accreditation in July 2009, according to the Massei report. It’s not clear when the accreditation process began, and it can often take a long time. It sounds possible from the Massei report (p. 206) that they were a year into the process when the knife was tested in 2008, but the wording seems ambiguous to me – it could also be that they had just started the process.

      In the former case, it should be expected that there exists documentation relating to ISO9001 setting out, in some detail, the procedures used in the lab and also how well staff were performing in terms of sticking to those procedures. For me, it’s the question of the existence or none-existence of that paperwork that is interesting, rather than the question of whether or not the lab held a certificate at the time.

  2. Catherine Shaw says:

    When you ask why the defence experts didn’t point out the potential errors in attributing peaks to stutter rather than actual genetic contributions, the answer is that in fact, they did point this out, in great detail. However, for one thing, being defence experts, they had less credibility than independent experts, and for another, they undermined their own credibility by attempting to claim that it wasn’t necessarily Raffaele Sollecito’s DNA at all, something Conti and Vecchiotti have not claimed.

    • maundy says:

      Hi Catherine.

      Yes, at trial, the defence experts did go into the issue of whether some of Stefanoni’s stutters were actually genuine alleles, but they did this on the general basis that it was all a bit subjective and so there was room for different opinions on the matter. The idea that there is a rigid formula for working it out seems to be something new that C&V have brought to the table.

      I’m not saying that the C&V methodology is bad, just that it may not be as widely practised as the review suggests, given that the defence experts don’t seem to have mentioned it last time round.

      • Catherine Shaw says:

        No, Tagliabracci in particular cited the same rules (recommendations of the ISFG, International Society for Forensic Genetics) as Conti and Vecchiotti are using now, and asked Stefanoni about them in court. His specific questions concerning specific peaks in the electropherograms are quoted in the Massei report; there’s plenty of intersection with Conti and Vecchiotti’s questions. Stefanoni responded that she of course knew about the ISFG, but that they were to be taken as guidelines, not rules. She’s right that they are not supposed to be used as rigid formulas, but they are right to question her for actually ignoring these guidelines completely in the case of every allele not belonging to Sollecito.

        I’m neither praising nor condemning Conti and Vecchiotti’s arguments (although they seem to raise valid points). I’m just saying that many of their arguments were already raised by defense experts at the first trial, but made little or no impression at the time.

      • maundy says:

        But the thing is, the way I read C&V, there should be no question of “intersection” with their findings. For them, there seems to be only one way to interpret the peaks. Tagliabracci most definitely does not follow the C&V school, because he wants to include peaks that clearly fail their test. So there’s a question about whether the defence still agree with what is attributed to him by Massei, that “there is a significant subjective element in reading the electropherograms”.

        I sort of agree that they are right (or, at least, within their rights) to question how Stefanoni’s exercise of her subjective opinion happened to iron over the peaks that were not convenient in terms of the match to Sollecito. But I also think it could be slightly question-begging. It could simply be that the subjective judgements were appropriate and sensible, and that we see the proof of that in the pudding.

        I agree that maybe I should be clearer in that ISFG was not unmentioned at trial, rather that the way it is used by C&V is a novelty of the review. To the extent that it was, there does not appear to be any difference of opinion between the two sides. They agree that it is subject to individual interpretations but differ (what a surprise) as to which individual interpretations should be preferred.

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