Monday, February 23, 2009

Understanding Micheli #3: Precisely How Damning Is The DNA Evidence?

Posted by Nicki

Here now is the full 2011 Micheli Report kindly translated by Catnip for the Wiki and TJMK.

1. The Context

Judge Micheli has had two very important roles. He presided over Rudy Guede’s trial and sentencing, and he presided over the final hearing that committed Raffaele Sollecito and Amanda Knox to trial.

Late January, Judge Micheli made public the 106-page report that explains the thinking behind both actions.

These four posts are examining several very key areas of the report so that we too may choose whether to buy into the rationales. I recommend watching this Powerpoint.

Click for Post:  Powerpoints #7: DNA Evidence - A Very Clear Intro To A Vital Subject Here

2. The DNA Evidence

Coming up soon is a more silent witness, one very important to both the prosecution and the two defenses: the extensive DNA evidence.

Specifically the DNA belonging to Meredith, Knox, Sollecito, and Guede, which was found at the scene of the crime, and on the suspected murder weapon found, apparently hidden, in Raffaele Sollecito’s house.

DNA of Sollecito has been found on the clasp of the victim’s bra. DNA of Amanda Knox was identified on the knife handle and also in the bathroom and Filomena’s room. DNA of Meredith DNA has been found on a knife compatible with the wounds that caused her death. DNA of Guede was found on the victim’s body and items and elsewhere in the house.

In summary, the biological sources and locations where DNA belonging to the victim and three defendants was found are these:

Guede’s DNA

DNA (from epithelial cells) was found inside Meredith, also on toilet paper, also on the right side of Meredith’s bra, also mixed with Meredith’s DNA on the her purse zip, and also on the left cuff of Meredith’s light blue sweater. Five total.

Sollecito’s DNA

DNA (from epithelial cells) was found on Meredith’s bra clasp, mixed with Meredith’s DNA, and also on one cigarette butt found in the kitchen. Two total.

Knox’s DNA

DNA (from epithelial cells) was found on the knife handle, and also close to the blade junction. DNA was also found in the small bathroom and in Filomena’s room

Meredith’s DNA

DNA was found on the knife blade. It was not possible to ascertain both the haematic and epithelial source of Meredith’s DNA on the knife blade, due to the scarcity of the sample. Numerous significant biological traces belonging to Meredith were found outside her bedroom - for example, DNA originating from the blood-trace footprints revealed by luminol found in Filomena’s bedroom, as reported at the Massei trial. Many instances total.

3. Defence Claims

Claims of contamination and “poor matches” of the DNA samples were raised by the Sollecito and Knox defenses, although not by Guede’s.

These claims had not been raised by the defenses’ experts who observed all the testing. 

4. Prosecution Rebuttal

The DNA expert Dr. Stefanoni’s arguments in reply to the defenses’ claims are summarized in Judge Micheli’s report.

Low Copy Number

Dr Stefanoni reported that the locus ascribable to Meredith and identified on the knife blade shows readings of 41 and 28 RFU.

Conventionally, RFU values lower than 50 can be defined as low. But she maintained that the profile matched Meredith’s by explaining that there is no immediate correlation between the height of the peaks obtained by electropherogram and expressed in RFU, and the reliability of the biological investigation.

In fact even if statistically - in most cases - the RFU data is directly proportional to the possibility of a certain interpretation of the analysis result, on the other side many cases of high peaks of difficult interpretation exist (because of background noises), as well as low peaks that are objectively unquestionable, hence the need to proceed to the examination of data that is apparently scarce, but that mustn’t be considered unreliable per se.

The use of multiplex PCR and fluorescent dye technology in the automated detection and analysis of short tandem repeat [STR] loci provides not only qualitative information about the profile - i.e. which alleles are present - but can provide also quantitative information on the relative intensities of the bands, and is therefore a measure of the amount of amplified DNA.

So if on one side Dr Stefanoni admits that the RFU readings are low, on the other her experience suggests that many cases of unquestionable matches exist showing readings lower than 50 RFU, and this appears to be the case with Meredith’s DNA sample on the knife.

Possibility Of Contamination

Contamination in the laboratory is categorically excluded by Dr Stefanoni. The samples were processed with maximum care in order to avoid any contamination during lab procedures. Defense experts observed all processing and nevr raised any objection.

Contamination during the collection phase is excluded by Judge Micheli, as the samples were collected by different officers at different times in different places (example Via della Pergola at 9:40am on Nov 6. 2007, and Sollecito’s apartment at 10:00am, on the same day, by a different ILE team).

As for Sollecito’s DNA found on the bra clasp, the match is unquestionable, according to the lab reports.

Samples from crime scenes very often contain genetic material from more than one person (e.g. Rudy Guede’s DNA has been identified in a mixture with the victim’s DNA in a few places), and well-known recommendations and protocols exist in order to de-convolute mixed samples into single genetic profiles.

So if the lab reports indicate that unquestionable biological evidence of Sollecito’s DNA was found on the bra clasp, at the present time we have no reason to believe that these recommendations weren’t followed and that therefore the reports are not to be trusted.

Conspiracy Theories

As to cells “flying around” depositing themselves - and their DNA content - here and there around the murder scene, there have been some imaginative theories advanced, to say the least.

The reality though is that although epithelial cells do shed, they don’t sprout little wings to flock to one precise spot, nor grow feet to crawl and concentrate on a piece of evidence.

There needs to be some kind of pressure on a surface in order to deposit the amount of biological material necessary to yield a reliable PCR analysis result.

A simple brushing will not do. 

As a matter of fact, Dr Stefanoni agreed with Guede’s defense that Guede’s genetic material found on the left sleeve of Meredith’s blouse was minimal; and this was because the DNA found there belonged to the victim and was not a mixture.

In the situation where there is a clear disproportion between quantitative data of two DNA’s coexisting in a biological trace, the PCR will amplify the most abundant DNA.

As agreed by Dr. Stefanoni and Guede’s defense, the conclusion here was that on the left sleeve there was plenty of Meredith’s DNA; but very little of Guede’s. This was used by his defense to deny that Guede had exerted violence on Meredith’s wrist.

5. Judge Micheli’s Ruling

After listening to the arguments of the prosecution and the defenses, Judge Micheli provided reasons why he rejected the contamination claims and ruled that all the biological traces identified as reflecting Sollecito’s and Knox’s DNA are admissible as evidence.

He arrived at the conclusion that the DNA evidence is sound and, considered along with the non-biological proof, he decided there was more than enough evidence to order Knox and Sollecito to stand trial.

6. Relevance To 2009 Trial

Regarding the biological significance of the traces, we are now looking forward to hearing the Knox and Sollecito defenses’ counter-arguments.  But as we understand it now, the DNA evidence for the trio having all been involved in the murder seems pretty damning.

The trial to establish the truth about the murder of Meredith continues next Friday. As we’ve reported, various human witnesses have already been heard from: the Postal Police who discovered Meredith’s body, Meredith’s two Italian roommates, and her seven British friends.


Many thanks for this! It’s really good to have some authoritative information about the hard evidence.

I’m sure everyone appreciates the huge amount of time and painstaking work that goes into writing a post like this.

Are you intending to cover other forensic evidence in future posts, such as the mixture of Amanda’s and Meredith’s blood in the bathroom, the various footprints, the evidence of clean-up and bleaching? Is information on this available in Micheli’s report?

Posted by GreenWyvern on 02/23/09 at 07:58 AM | #

It’s good to see the evidence explained by an expert in DNA AND an expert in Italian law, it makes all the difference when trying to get your head around what is going on!

Posted by daisysteiner on 02/23/09 at 02:30 PM | #

Hi GreenWyvern,

It is surely a very strange coincidence that Amanda blood was found in the bathroom mixed with Meredith’s just after the murder. However, strictly from the biological point of view, these traces are not very significant because it is not possible to date blood with great accuracy. Of course there’s a difference between freshly deposited blood, and a spot that has been sitting for many hours, but the time range here is much wider.

There’s hardly any information about the clean-up in Micheli’s report. About the footprints, Micheli doesn’t attach much weight to them, except that they prove that more than one assailant was present - however he feels the issue will have to be further discussed in Court of Assise.

Posted by Nicki on 02/23/09 at 05:15 PM | #

Nicki, thank you. I have no expertise in biology and appreciate the effort you have made to clarify these issues. If I have understood correctly, this sentence is key: “So if on one side Dr Stefanoni admits that the RFU readings are low, on the other her experience suggests that many cases of unquestionable matches exist showing readings lower than 50 RFU, and this appears to be the case with Meredith’s DNA sample on the knife.”

Also important for our understanding of this case is that, although the defense teams have repeatedly argued on the basis of the mere possibility of contamination (either in the laboratory or at the point of collection), and while this possibility ALWAYS exists to some extent, there is no reason to think that the samples here were contaminated at either stage. It is only logical that the mere possibility of contamination per se is not a valid legal argument for rejecting the results of these tests or any other tests, unless there is some other compelling reason to do so. Otherwise, what would be the point of using DNA in criminal cases at all? This may explain why there was such an effort on the part of Sollecito’s defense to prove contamination at the point of collection.

If I understand correctly, DNA testing is often used to rule out certain hypotheses. In this case, the DNA results do not allow us to rule out the suspects.

You also wrote: “As to cells “flying around” depositing themselves – and their DNA content - here and there around the murder scene, there have been some imaginative theories advanced, to say the least. The reality though is that although epithelial cells do shed, they don’t sprout little wings to flock to one precise spot, nor grow feet to crawl and concentrate on a piece of evidence.”

This seems particularly applicable to the existence of Meredith’s DNA inside a groove near the tip of the blade of the knife. How likely is it that someone cleaning a knife (with bleach) would accidentally deposit the epithelial cells of a person who had never visited the apartment where the knife is being cleaned? Even if we accept the hypothesis, however far-fetched, that Knox or Sollecito served as the transport system for skin cells belonging to Meredith, how likely would it be for these cells to detach themselves, fly around Sollecito’s flat and land inside a groove on a knife?

Posted by Skeptical Bystander on 02/23/09 at 06:14 PM | #


Not being a scientist or a lawyer myself, it has taken me quite a while to read and understand your concise information and explanations.  I thank you for giving me/us yet another tool to try to piece together the evidence and wade through the hyperbole from the defense.  Much appreciate your efforts here.

Posted by jodyodyo on 02/23/09 at 09:31 PM | #

Excellent job of describing this key forensic evidence.  Meredith was an exceptional person who would, and did, fight to maintain her moral integrity.  She had her beliefs and chose to not just talk the talk, but to walk the walk.  This is the kind of stuff for which the military gives out medals; it took tremendous courage and conviction to stand up against three armed people.

DNA has been found on a cigarette butt and on a bra clasp.  What is puzzling to me is the following:  We know the fight took place but why isn’t there MUCH MORE DNA?  I was thinking it would surface at the trial and the DNA we know about what just the tip of the iceberg.  It does not appear that the bedroom was cleansed as was the rest of the house.  Is it possible she was dragged into the bedroom after an attack that actually took place outside the bedroom?  This would have been in an area that had been mopped and would explain why it was necessary to clean the area outside the bedroom at all.

One other thing.  Amanda’s description of how she stood in the kitchen covering her ears to drown out the screams as Patrick L. attacked her was incredibly graphic.  Perhaps, the only part that was a lie was the Lamumba part.  This has always bothered me.  This is one description of events that was in extreme detail, unlike most of the others.  I have trouble believing that someone, even someone as creative as Amanda, could have made that up while being interrogated.  She’s good, she’s very good.  But I don’t think she’s good enough to dream that up.  Maybe it actually happened.

Posted by Arnold_Layne on 02/24/09 at 03:50 AM | #
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