LCN DNA analysis
Fiona,
In your comment on the DNA on page 6, part 1a, you wrote, that Dr. Stefanoni is an “internationally respected forensic scientist.” Can you support your statement?
You wrote “There was not a big enough sample to allow for a re-test. That is certainly a problem, but it is not enough to overturn the finding.” It is important to bear in mind that low copy number (LCN) DNA profiling was the technique used on the knife: “Because LCN analysis by its nature is not reproducible, it cannot be considered as robust as that associated with conventional DNA typing.”
http://www.denverda.org/DNA_Documents/CMJ Budowle.pdf
But the problems with LCN and Dr. Stefanoni’s protocols are more serious. The following paragraphs are from
http://www.sciencespheres.com/
Even with those far more stringent protocols, LCN profiles are not allowed as evidence by the vast majority of the world's courts. But let's take a look at these proposed procedures that attempt to place LCN testing on a more reproducible, reliable basis. That way, we can illuminate the deficiencies in Stefanoni's science improv technique.
The following quotes are all from the Crown Prosecution Service in the U.K. at:
http://www.cps.gov.uk/publications/prosecution/lcn_testing.html This is from an article that supports the use of LCN.
“The FSS LCN test requires an ultra-clean laboratory and so is more expensive and less widely offered than the standard test.... 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.”
Stefanoni's procedure, in sharp contrast to these requirements, was performed in an ordinary DNA analysis laboratory with other DNA units present. An ultra-clean laboratory, positive air pressure systems, and photo and chemical DNA sterilization are vital techniques to avoid contamination of samples within the laboratory. None of these facilities and procedures appears to have existed for Stefanoni's test. That makes four more technique deficiencies.
“In LCN testing, each sample is divided into three parts or aliquots, and two of these are tested. The third is retained for further testing in the event of a failure or to confirm the presence of a mixture.... Only those DNA components that are seen twice are included in any calculation, to show that the result is reproducible.”
Stefanoni used 20% of the sample to test for blood, which came out negative. Whatever was on the knife, it wasn't Meredith's blood. Then she tested all of the remaining material at once, so there was no possibility of comparing two results, and nothing left for further testing. By the standards of the Crown Prosecution Services, Stefanoni's results would be thrown out by either of these criteria. And that makes two more deficiencies.
[End of Quote]
You wrote “One may regret the lack of a retest but it does not seem that the defence are arguing that the dna was not there at all.” I find this statement absolutely bewildering. The point of doing a retest is to see whether the DNA is really there or not.
You wrote “She said that there has been no instance of contamination of this sort in her lab in the last 7 years. She pointed to the fact that no DNA from any of her team was found on any of the objects tested:” But Dr. Stefanoni did not perform negative controls, or if she did, she did not report them. You also wrote, “the knife was found and put in a plastic bag, which was then put into a box. There does not seem to be any possibility of contamination at that stage” However, the US department of Justice advises, “Put evidence into new paper bags or envelopes, not into plastic bags.” (
http://www.ncjrs.gov/txtfiles1/nij/bc000614.txt)
Dr Waterbury summarizes (
http://www.sciencespheres.com/) the problems in the LCN DNA analysis of the knife:
So we see that in roughly nine distinct ways, Stefanoni's improv LCN DNA profiling was even worse than unproven and inadmissible LCN DNA profiling tests.
1. The DNA wasn't amplified enough; the very weak fluorescence was simply blown up.
2. The test site was not remote from other DNA tests to avoid contamination.
3. Specialized LCN-quality entry procedures to avoid contamination were not used.
4. A positive pressure environment was not maintained to exclude contamination.
5. Special LCN sterilization procedures to destroy errant DNA were not used.
6. The entire sample was consumed in a single test; no comparison of tests was possible.
7. No sample was retained for future reference. The test can never be reproduced.
8. No negative control tests were run to check for contamination.
9. No control tests to check for field contamination were performed.
[End of Quote]
Now let us turn to the open letter signed by nine DNA experts and see what they say about the knife. A pdf file can be found here:
http://www.friendsofamanda.org/articles.html
They say that it is unlikely that the knife could be cleaned of all traces of blood yet retain enough DNA to produce a profile of the victim. They discuss that the highest peak in the electropherogram is only about 100 relative fluorescence units with many falling between 20-50. They note the lack of ability to reproduce this result, and they also note that electronic files that would allow independent analysis of the data have not been disclosed. They conclude, “No credible scientific evidence has been presented to associate this kitchen knife with the murder of Meredith Kercher.”
If someone wishes to dispute the scientific validity of the statements I have presented by quoting the comments of other scientists, I would be interested in hearing it. I will save the discussions of Sollecito’s explanation and of the bra clasp for future comments.
Chris
