Anyone wanting a walkthrough of the DNA process and Stefanoni's curious methodology and what that actually
means should try to digest
this post first. That has an explanation of the process, fully linked and cited, with videos so you can see what these machines look like and how they're used, along with the instruction manuals and further citations from the FBI, Massei, C&V and the Hellmann reports. On that post one should follow all the links, starting especially with those pages from the FBI report to get an overview of this process and the importance of doing it right and what Stefanoni actually did.
From Math on Trial with my comments inserted:
Maths on Trial said:
According to her testimony, Dr. Stefanoni began by unpacking the knife from its wrappings and examining it under a strong light. She perceived a few streaks on the blade, perhaps indicative of vigorous scrubbing. She took swabs along these streaks, managed to obtain an infinitesimal quantity of biological material— human cells, in fact, but precious few of them
This may have been her testimony but it is untrue (a significant cause for alarm, one might think). As Conti-Vechiotti point out:
Conti-Vechiotti said:
Originally Posted by C-V
It must be emphasized that no laboratory tests were performed to detect biological material of a non-haematic nature on any of the samples analyzed.
It is considered that it would have been necessary to proceed to morphological tests to identify cells which might have been present, by means of colouration with one of the reagents commonly employed in histology (hematoxylin). Such a test, quick and easy to carry out, would have required a minimum quantity of material and would not in any way have compromised further laboratory testing, but could have clarified the nature of the material removed from the item under examination.
Despite the negative result of the blood identification test and the failure to carry out cell identification tests (and therefore the failure to identify the material removed from Exhibit 36) the Technical Consultant hypothesized the presence of “presumed exfoliated cells” on the material sampled from the knife handle (traces A-D-F) and of “presumed biological material” of another nature (presumably blood, considering the tests aimed at the detection of haematic peroxidases) on the material sampled from the blade (samples B-C-E-G).
Maths on Trial said:
— and proceeded to perform two analyses on it: one to determine whether or not the cells were blood cells, and the other to obtain a DNA identi- fication.
Also incorrect. She performed a blood test - negative, a species specific test - negative and DNA quantification, falsely recorded as positive but in fact negative.
Maths on Trial said:
She also swabbed the handle of the knife. The DNA on the handle turned out to be Amanda’s, but this was not considered incriminating, as she had used the knife while cooking at Raffaele’s house. The DNA on the blade, however, was a different story. The first test could not establish whether or not the cells were from blood. They were human cells, but they might have been from skin or tissue.
Incorrect. No human cells were detected in sample 36B.
Maths on Trial said:
For the second test, Stefanoni’s machine was set up to work with a minimal quantity of biological material that was significantly greater than what she had at her disposal. At first this machine simply output “too low,” indicating that using the standard settings it was not able to analyze such a tiny quantity. Many forensic geneticists would have followed the accepted rules and stopped the analysis at this point. But Stefanoni elected to continue, modifying the settings and pushing the machine beyond the limits recommended in the manufacturer’s guidelines. By doing this she managed to obtain a DNA profile for the cells on the knife.
Incorrect. The Qubit fluorometer yielded one result only - too low - as it did for sample C which Stefanoni ceased to process further. Schapps thinks the Qubit fluorometer is itself used for generating DNA profiles, ignoring altogether amplification and electrophoresis in which it plays no par at all. She has over-simplified and elided crucial steps in the process to such an extent as to render her opinion worthless. She finds no room to mention the significant falsehoods retailed by Stefanoni when giving evidence and in her records. These are not matters for mathematics but for forensics.
Great post, Anglo! You can add this part regarding what the actual scientists thought of Stefanoni's 'hypothesis' regarding what she found:
C&V Report Assessment of the Forensic Genetic Tests Conducted by the Scientific Police on Item 36 said:
From what has been set forth above, we hold that the documentation in the case file reveals inaccuracies and gaps about the analytical procedures performed on Exhibit 36.
In particular:
- regarding the nature of the material collected,
there is no scientifically conclusive evidence to support the possible blood nature of sample B (knife blade) in that both the generic blood test and the human species test were negative.
The
existence of presumed exfoliated cells on the samples taken from the knife handle is
equally lacking in scientific basis.
Therefore we repeat that the theories formulated by the Technical Consultant about the nature of the material removed from Exhibit 36 are wholly arbitrary in that they are not supported by any objective confirmation.
(emphasis retained)
This was an
egregious error on the part of the author of "Maths on Trial," not very
thoughtful of her. Stefanoni didn't actually find any cells, she 'theorized' that there were some there--and they were blood--despite the sample failing
two highly sensitive blood tests and her not testing the samples further to attempt to identify the substance, which may have been nothing--or nothing but starch--as far as anyone knows.
Also, the issue with the knife (and to an extent the clasp) is
not (simply) one of probabilities regarding the DNA matching, but
even if that sample was handled perfectly and all requirements were met for scientific validity thus the DNA
was a match as best as can be scientifically determined, the issue comes down to whether the result was obtained due to contamination or fraud--the likelihood of it being due to the knife being used in the murder is so remote it's not worthy of consideration.
There's four basic possibilities of how that DNA result may have been obtained:
1.) Contamination: the sample was contaminated inside the lab in the process of Stefanoni testing some 3-400 items with Meredith's DNA and her lab not being properly equipped to handle LCN DNA which requires much stricter standards because they're
looking for contamination-level DNA. In addition, the fact that Stefanoni never quantified or identified any substance supports that conclusion as that would be the case if the contaminating DNA was the result of the amplification process, which replicates DNA but
not human cells or biological material.
2.) Fraud: The sample never contained anything and she knew it, she just produced a electropherogram from another sample she knew had Meredith's DNA in it. This would explain her bizarre procedure in which she (supposedly) got a negative ('too low') from the handheld Quibit Fluorometer (a quantifier which will measure the amount of DNA) but ran the sample anyway
without amplifying it 31 (or more) times as the literature from the kit explains and then
not using Real Time PCR (which she did for all the rest of the samples--even negative ones--
anyway) which would have given her the quantity of the sample she was testing. Not being able to quantify the substance is also suggestive of contamination, though her inexplicably ignoring the 'too low' negative and then
avoiding Real Time PCR is more suggestive of fraud or incompetence. Not amplifying the sample more than 28 times is also suggestive of incompetence if she actually proceed the way she claimed in court. Once she knew she was testing a sample that was 'too low' she had to realize it would be
by definition 'Low Copy Number' or 'Low Template' DNA.
3.) Secondary (or tertiary) transfer. Meaning there actually was a handful of picograms on the knife blade, but it was the result of Amanda (or theoretically Raffaele) having touched Meredith or something of Meredith (skin cells) was on their bodies or clothes and they touched the knife, or they touched something Meredith touched. For example Amanda might have dried it off on her sleeve as she put it away and her clothes had miniscule quantities of Meredith's DNA on it. If the result was not because of contamination or fraud this is the most likely explanation for Meredith's DNA being on the blade for
numerous reasons, mainly being there is
absolutely nothing else forensically that suggests that knife was used in the murder and a few very good reasons to believe it wasn't.
4.) The knife was used in the murder. This one faces a number of obstacles, mainly being the knife did not match the wounds nor the outline left on the bed, plus it was tested
extensively for blood not just by Stefanoni but also Conti & Vecchiotti with negative results. The idea that every last trace of blood was scrubbed from the knife but that some DNA of Meredith's was left on the blade and plenty of Amanda's DNA on the handle is
damned silly. Basically impossible, DNA you can extinguish with a spray bottle, blood can be detected even on clothes that have been washed, for crissakes it might leave a visible
stain if not done thoroughly enough!
Just one last note on what most people think of DNA evidence and the difference in the DNA evidence in this case. What is usually presented (almost always in British or American courts) as DNA evidence is that process
identifying the person who left whatever
incriminating substance that was found at a crime scene. For example investigators find a bite wound, they test it for saliva and if they obtain a positive result they determine that it was so-and-so. Or perhaps they find skin under the fingernails of the victim, or semen in the case of rape, all of which are highly suggestive they were involved in the crime. They don't just find
trace elements (LCN/LT DNA) and then go 'presuming' they were the result of the murder, because those sorts of trace elements are so easily transferred in non-incriminating ways.
In this case there's so many reasons to think that knife was
not involved in the murder, the
real question is how was that DNA result obtained. If they'd found Meredith's DNA under the refrigerator would they think the fridge was involved? If they found it in a goldfish bowl would that implicate the goldfish? No, those one can just dismiss with an eyeroll, however the same is conceptually true of a knife found in a drawer a quarter-mile away from the crime scene that tested negative for blood and was too big to cause the wounds.