Friday, May 29, 2009

DNA Evidence: The Myths Start To Come Crashing Down

Posted by Nicki

[click for larger image; rule and annotations by Kermit]


The DNA evidence is proving to be as well-handled and as incriminating as DNA evidence ever is at such trials.

The last two hearings have very publicly exposed several of the key myths which have been aggressively propagated over the Internet and through other media for many months.

Let’s first speak about the double knife DNA. It has now become pretty obvious that:

  • It doesn’t match half of Italy as falsely claimed
  • It doesn’t have a 20% chance of being Meredith’s as falsely claimed
  • Stefanoni never declared herself that the DNA “was unreliable” as falsely claimed
  • The DNA has not been amplified “500 times” as falsely claimed

Patrizia Stefanoni has not stated that Meredith’s DNA was extracted 500 times from the knife sample, as some people with what seemed a google-level knowledge of molecular biology were claiming to muddy the waters.

The DNA was actually extracted 50 times from Meredith’s specimens and was used to compare it to other biological traces, including the one found on the knife. And it provided the forensic team with good samples to be compared to the traces found on the knife.

Two genetic profiles are identical and therefore belong to the same individual if a) they are in the same position, and b) they have identical shape and dimension. In this case, each peak produced in the original samples exactly corresponds to the peaks yielded by the knife sample, position, shape and dimension”¦ Say so long to the “matching half of Italy” myth!

Furthermore, Stefanoni excluded any possibility of contamination in the lab, stating that it had never once occurred in her lab for at least the last seven years, and every precaution was taken in order to exclude possibility of contamination so that different traces are not mixed. 

Contamination during the collection phase was also excluded: the forensic team that found the knife was a different one from those who searched the cottage, so how could Meredith’s DNA possibly have been “transferred to the knife”? 

Furthermore, the knife was put in a shoe box after it was bagged, and it stayed there until it reached the lab. And once again… DNA doesn’t fly, it doesn’t creep, and it sure doesnt penetrate a plastic bag!

Now let’s speak about the bra clasp.

The DNA found on the clasp has been defined as abundant and identified as belonging to Sollecito without any doubt. It should have been collected earlier in the process, but DNA evidence is often collected weeks or months after the crime when an object involved is unearthed.

The chances that it has been contaminated are at zero: the sample was found under the pillow on November 2, during the first search, and collected on December 18th when the second search took place by a different team.

During this entire time, the clasp was laying on the floor of what has been testified to have been a completely sealed crime scene. So when and how could any contamination occur?

Excluding a spontaneous migration of Sollecito “˜s DNA on the clasp from some unidentified location in the murder room or in the cottage, it could have only taken place during either the first or the second handling of the sample, so the fact that the clasp was recovered weeks later really bears no relevance.

And additionally, where could any abundant amount of Sollecito “˜s biological matter come from, if besides that on the bra clasp, the DNA corresponding to his genetic profile was only found on a cigarette butt? 

Perhaps this is why Sollecito’s lawyer Ms Buongiorno is now claiming that the bra clasp was contaminated in the laboratory. She is reduced to having to claim that in effect Dr Stefanoni applies strict laboratory procedures when testing Guede”˜s or other peoples’ specimens, but somehow miserably fails when the samples belong to Sollecito and Knox.

Finally, let’s not forget that Rudy Guede’s DNA was not found “all over” the victim, but only on the right side of her bra, on the left cuff of her jumper, and inside her body. If passive transfer of DNA is so easy to happen, and if Guede is the only one who physically attacked Meredith, how comes his DNA was found only in these three places on the victim’s body?

DNA is NOT easy to transfer. Dr Stefanoni is absolutely correct when she says that “transfer of DNA must not be taken for granted nor it is easy to happen, and more likely to take place if the original trace is aqueous, not if it is dry”.

About the possibility of contamination having taken place in the lab, this is a risk that everyone working with PCR is well aware of. It is certainly not probable that it could occur every time a biological sample is tested. In fact, it is very unlikely to happen when the routine strict precautions are taken.

And there is no doubt that Dr Stefanoni was extremely cautious when handling any of these samples. 

I can see the reason for the improbable reach of the defense teams: since their clients deny any involvement, the positive DNA results “must” be contaminated - what else could they possibly say? Regarding this evidence, it is the only argument that they have available.

Finally, Dr Stefanoni has an international reputation and is considered one of the best in the field today. Questioning her credentials really makes no sense at all. But those too have come under attack.

Edited to add: On the issue of DNA transfer, from today’s hearing (La Nazione)

“The contamination theory has been discussed again today: Ms Bongiorno repeatedly asked the forensic witnesses information regarding the techniques used to collect the samples found in Meredith’s house, but PM Manuela Comodi showed the Court that contamination did not occurr by asking the forensic witnesses: “Using the same gloves, you have touched the victim’s socks after working on other samples. Could you tell me what the result of the sock analyses was?”

The witness answered:  “No foreign DNA nor genetic traces have been found”. Another demonstration that DNA passive transfer just doesn’t occur so easily.  Differently, the probabilities of obtaining a contaminated sample would be so high that DNA testing would hardly be of any use in crime investigations.




Comments

Nicki, thank you again bringing clarity to such a technical and difficult subject to understand.

Your expertise in the field of DNA is much appreciated! 😊

Posted by Tara on 05/29/09 at 06:12 PM | #

The knives resting in my kitchen block look nothing like this one. 

This knife appears to be more like a hunting knife used by mostly burly men who don’t sit around Richie Ritches house with their dog Dollar having NOTHING ELSE BETTER TO DO than get high and read porn comics.

I still feel Knox used this as her weapon of choice mainly due to a dare by the owner of the knife - for her to use it in the manner for which it was made.  As a hunting knife.

RIP Meredith Kercher

Posted by Professor Snape on 05/29/09 at 07:09 PM | #

Thank you Nicki for explaining what’s really been happening at the court hearing regarding DNA.

Posted by Jools on 05/29/09 at 08:42 PM | #

Ciao Nicky,

Highly appreciated! Thanks.

Fiori

Posted by Fiori on 05/29/09 at 11:27 PM | #

It looks very much like a kitchen knife to me; I have one almost identical in my kitchen.

Over here doctors have been calling for such knifes to be redesigned so that they have rounded end. There is no real need to have a long knife with a sharp point for domestic cooking. The problem with these knives is that they leave deep puncture wounds which are very damaging to internal organs.

Posted by bobc on 05/30/09 at 02:42 AM | #

Thanks Nicki! 

Of course the defense must resort to the bogus and tired claim of contamination because their clients have no alibis!

Posted by Jumpy on 05/31/09 at 09:39 AM | #

Does anyone know if the knife was actually hidden (ie deliberately concealed) in Sollecito’s apartment. At first I heard it was found in a shoe box but having read the above by Nicki it seems it was collected and placed in a shoe box.  Many thanks for all the fascinating insights.

Posted by pensky on 06/16/09 at 07:52 AM | #

Hi Pensky,
The knife was not concealed in a shoe box, it was found in a drawer in the kitchen, collected, bagged, and finally put in a carton box.

Posted by Nicki on 06/16/09 at 11:08 PM | #


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