On the eve of the verdict of the high-profile trial in Perugia, Italy, in which Amanda Knox and Raffaele Sollecito are charged with the murder of British student Meredith Kercher, DNA evidence brought by the prosecution is being questioned by nine US specialists in DNA forensics.
The trial is in its final stages, with a verdict expected on 7 December. Knox and Sollecito are pleading not guilty. In an open letter, the US specialists outline their concerns with two pieces of DNA evidence that are central to the case against Knox and Sollecito.
The defence has already suggested that the amount of DNA allegedly linking the pair to the crime is too small to be definitive. The letter raises the possibility that this DNA was introduced through contamination of the evidence and concludes that the DNA test results "could have been obtained even if no crime had occurred".
Two years ago, Kercher was found dead, with cuts to her throat, in the accommodation she shared with Knox in Perugia. Although a third suspect, Rudy Guede, has been convicted of her murder, the prosecution claims that Knox and Sollecito helped.
Knife recovered
The case against them largely hinges on two pieces of DNA evidence. One is from a knife recovered from the kitchen drawer at Sollecito's apartment. The other comes from a portion of a clasp that was cut away from the bra Kercher was wearing. The forensic specialists question both.
In respect of the knife, the letter says contamination from other DNA present in the lab that did the analysis cannot be ruled out. The initial method used was standard: the DNA was amplified, then analysed using electrophoresis. This generates a graph consisting of a series of peaks, whose heights represent how much of certain DNA snippets are present. Taken together the peaks create a DNA "fingerprint" unique to an individual.
The lab says that DNA taken from the knife's blade produced a series of peaks that matched Kercher's DNA, while DNA from the handle produced peaks that matched Knox's.
To minimise the risk that some peaks arise from contamination, most US labs only count peaks falling above a height threshold of 150 relative fluorescence units (RFUs) and all dismiss those below 50. The trouble with the DNA found on the knife is that "most of the peaks are below 50", says Greg Hampikian of Boise State University in Idaho, who signed the letter and reviewed the DNA evidence.
Contamination fear
When this happens, samples can be rerun, but this doesn't appear to have been done in the Knox and Sollecito case. This means contamination cannot be ruled out, the open letter claims. The same lab may also have been running DNA profiles from other evidence in the case at the same time, it says, and tiny amounts of this could have contaminated the knife samples.
What's more, a sensitive chemical test for blood on the knife was negative, and it is unlikely that all chemically detectable traces of blood could be removed from the knife while retaining sufficient cells to produce a DNA profile. "No credible scientific evidence has been presented to associate this kitchen knife with the murder of Meredith Kercher," the letter concludes.
Evidence from the clasp is equally inconclusive, according to the letter. What looks like a mixture of different people's DNA was found on it, and Sollecito could not be excluded. However, because Sollecito had visited the women's home several times before the murder, his DNA could have made its way onto the clasp "through several innocent means", the letter says.
Neither Sollecito's nor Knox's DNA was found on the remainder of the bra, other items of Kercher's clothing, objects collected from Kercher's room, or in samples from her body – although Guede's DNA was found everywhere, the letter points out.
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Have your say
I'll be honest, due to Knox' intereactions with the press always smiling, I wasn't convinced she didn't have anything to do with it... however I reserved my opinion as I didn't have even a smidgeon of the facts.
If what is stated in this article is true, the italian police look to be in full swing of the standard european police mode of kneejerk reaction.
If these two genuinely are innocent then I hope that the people on the jury are intelligent enough to see through the prosecutions' need to not look like twits.
just to clarify, continental european criminal law does not depend on just the jury to reach a verdict. There are one, three or five judges (depending on the severity of the case, with some rare occasions even having seven) and the jury size is reduced compared to the american and british systems. The verdict is reached by a vote of both the judges and the jury. If there is a tie, it is usually resolved by the vote of the court's presiding judge.
I think this is a sweeping generalisation. "Continental Europe" is made up of many countries and I am fairly confident they each have their own judicial processes. To lump them all together as one is somewhat ill-informed.
Well, the term is a contrast mainly to the UK, and it is reasonably well established. As for their judiciary systems, they follow variations of civil law (as opposed to common law, in the anglosaxon countries) which are based on the same procedure. The only things that may change are the required severity to have three or five judges. If you check wikipaedia for civil law, it has a nice map with its prevalence.
If one regards the television episodes on the USA network, it is plain to see that Framers of depraved crime plant evidence of innocence everywhere before their plan of becoming guilty, because they believe that they are better than us all.
Thank God, we are better than them.
New Scientist, whoever we may choose you to be, you always solve problems in the best possible, logical way, with the fewest ignorances of the infinite variables which factor in and out at all times.
I will be a depraved crime-fighter.
Nine-eleven hit me hard. God save me, save me with all the particles that you possess.over this critical thing I find myself in: Time.
God, Freeze my shimmering blazes, of Rage.
God particles, hear this: I believe that you possess an ability to stop Time. Time speaks fast; Time speaks for all of us.
Newest Scientist, might you agree?
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I know they are specialists in their field, but were they asked to review the evidence, and did they have access to all of it? Just seems weird that they are disputing evidence in a case they don't seem to be involved with, otherwise, why send an open letter and not testify?
Doesn't anyone think that it's weird that a trace amount of Knox's DNA is found on a kitchen knife from her own kitchen? Perhaps she used it once or twice (or it was in a drawer with other items that she touched).
And the case against the other defendant seems equally thin. The convicted Murderer's DNA was found all over the crime scene. You would think that there would certainly be more DNA from the defendants in this case, if they had actually participated.
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