The wonderful world of DNA
BobTheDonkey,
Here are some of your comments about DNA and my replies.
“It's really not that simple, however. Sure, the bra clasp handling was less than proper. HOWEVER, that in and of itself does not provide a means for contamination of a level we see on the clasp. That is paramount to the contamination discussion.” (message #11257, p. 282)
Your argument implies that you would not throw out a given piece of evidence solely on the basis of bad handling. One problem with this point of view is that there is no disincentive for carelessness in your system. Rules become only suggestions. Why should the technicians take the trouble to do it right if they are not held accountable when they do it wrong?
“If we accept that contamination did happen to the clasp DNA, then why is Sollecito's DNA in a higher concentration than that of anyone who had much more access to the room than Raffaele? Why is it Raffaele's DNA and not any of the investigators/forensics teams/roommates of Meredith who either had reason to be in Meredith's room or directly had contact (albeit, wearing gloves, etc) with the clasp.” (message #11257, p. 282)
Your only source for arguing that the amount of DNA was too large to be the result of contamination is Stefanoni, who does not publish any original research in DNA forensics. Can you find a literature citation that supports your argument? On the other hand, I have provided information from those who do publish, and they contradict Stefanoni’s claim, which you are repeating. Moreover, you are sidestepping the fact that Raffaele’s profile was at least sixfold lower in concentration than Meredith’s profile. There is no reason to draw a conclusion out of Raffaele’s profile being higher than that of the three unknown depositors while simultaneously ignoring why it is lower than Meredith’s.
“And, yet, the DNA profile from the knife is an incredibly close match to Meredith's. So are you claiming contamination? If so, where?” (message #11505, p. 285)
“Look, we've been over this time and again on this thread. There is absolutely no reliable source of contamination for the clasp and/or knife. None. The closest you can come up with is "contamination in the lab". And that's ignoring that the equipment used to test the knife had never been used before. And ignoring (ironically enough) that there was a 46 day lag between when the cigarette and other sources of Raffaele's DNA were collected and when the clasp was collected.” (message #12107, p. 303)
“So, if there were only two pieces of evidence/swabs from the cottage that contained Raffaele's DNA, how did the contamination occur?” (message #12028, p. 301).
With respect to the knife, the citations I have previously given indicate that Meredith’s reference sample and other pieces of evidence with her DNA are plausible sources for contamination. The document Charlie provided shows that there were many items in the lab with Meredith’s DNA (
http://www.friendsofamanda.org/selected_dna_test_results.pdf). There was no blood on the knife, and there was no evidence of other cells. Unless one believes in magic cleaning fluid that can remove blood cells but not other cells, contamination is the only reasonable explanation for the DNA on the knife.
With respect to the bra clasp, your argument falsely equates the objects that were found to have Raffaele’s DNA with all objects that had his DNA. Upthread katy_did noted that one or more towels would have had his DNA if he had washed there (he cooked for Amanda there, IIRC, so it is reasonable to assume that he washed his hands there). Any single sample from a towel might or might not show his DNA, depending on where it was sampled.
One route of in-lab contamination would be for the technician to handle the cigarette butt then to handle the clasp. A magnifying lamp was shown to pick up DNA in one study. Another problem with your comment is that it ignores the fact that DNA persists (see below).
“However, no explanation for how that contamination happened in this case has been forthcoming.” (message #10154, page 254)
“All you can do is provide bare assertions. Can you provide a plausible means of contamination for the bra clasp? Where was the primary transfer, Bruce? Where was the secondary? Can you provide a study where tertiary and quaternary transfer was validated? Then you have no real argument against the bra clasp.
“Moving on to the knife. The memo I was provided by one of you guys and subsequently quoted included a study from 2002 (I believe it was 2002) that indicated a full DNA profile could be recovered from a single cell using LCN processes. Given that there were more than a single cell and Stefanoni has been performing LCN testing for a number of years, there is no reason to suspect the DNA on the knife is not Meredith's. The only argument you have been able to provide is contamination - and yet when pressed, are unable to provide a plausible contamination scenario. Especially when we take into account that the knife was tested on a machine that had not been used before. Additionally, one of the suspects verified the likelihood of Meredith's blood on the knife, providing a completely implausible scenario for it's presence. So why should the knife evidence not be considered valid?” (
http://www.internationalskeptics.com/forums/showpost.php?p=5958420&postcount=13)
Do you have evidence that the machine had not been used before? Fulcanelli asserted this without backing it up. Can you document that Stefanoni’s lab was properly equipped? “The site of this bespoke laboratory is remote from other DNA Units, operates stringent entry requirements, is fitted with positive air pressure and specialist lighting and chemical treatments to minimize DNA contamination.”
http://www.cps.gov.uk/publications/prosecution/lcn_testing.html
LCN is done with at least two replicates, and only those alleles that show up in both runs are scored: “In low-copy-number profiling, forensic scientists generally split their limited amount of DNA into two or three samples and run analyses on two of them. The third, if available, is reserved for the defence. The results of analyses aren’t completely reproducible, profiles often won’t match and the scientists generally accept as true those STR signals that show up in both runs.” Nature (London) 464(7287):347-8 (2010), emphasis added. We can have a lively debate about the science behind using duplicate analyses, but what is not disputed is that Stefanoni didn’t do one. In addition, her pseudo-LCN technique has not yet been scrutinized in a peer-reviewed journal.
Your position is that contamination must be proved by a specific route. This is in opposition to everything I have read (
http://www.scientific.org/tutorials/articles/riley/riley.html). If your standard were adhered to, the contamination defense could not be used even in cases where it has happened. A specific route was not found in the Leskie case, nor in the case of Farah Jama, both of which I have previously documented. Here is another link on the Jama case:
http://www.abc.net.au/rn/lawreport/stories/2010/2895256.htm
Reagent blank (negative) controls can sometimes detect contamination, just not always. When assuming that contamination did not occur leads to an absurdity, then one accepts that DNA contamination has occurred, such as in the Mixer case:
http://www.garyisinnocent.org/web/CaseHistory/NewDNAFindings/tabid/58/Default.aspx
In many instances of contamination evidentiary items were processed at the same time. Yet, Dr. Theodore Kessis stated, “It must be noted however that contamination errors have been documented where no direct processing link between sample and contaminant have been established, raising the specter that a source of contamination can linger in a laboratory for some time.”
“I trust Stefanoni” (message #4895, p.123).
Even though she said that skin cells don’t contain DNA? Even though she made an inference about how the kitchen knife was used from the place where she found DNA on the handle, an inference I have not seen from any other forensic scientist? These are some of the reasons I do not.
But the problem with your statement is more general than whether or not one trusts a particular laboratory. Your position amounts to this: when the prosecutor walks into a courtroom and says I have DNA evidence, you want to give the jurors permission to shut their brains off. I don’t.
halides1
