Sampson,
Thank you for posting that quotation. There are some problems in the reasoning employed, and it might be worth one’s while to examine them.
First is the question of what is meant by reliability or unreliability of a DNA profile in the context of forensics. It has been known for more than twenty years that one can use the polymerase chain reaction (PCR) to obtain DNA profiles from as little as one or two cells (I posted this information many continuation threads ago). Therefore, it is no surprise whatsoever that the Carabinieri were able to obtain a profile.
Second is the question of how the test was performed and reported. From what I recall, the Carabinieri created a consensus profile from two amplifications, whereas Stefanoni did just one. Someone else may know better than I do, but didn’t they also deposit electronic data files? In addition Stefanoni’s lab was not even certified for standard profiling at the time. I am not sure about the forensic lab of the Carabinieri, but for argument’s sake, let us say it was. A third problem is that low template work should be done in dedicated facilities, not in the same lab as the regular testing. These problems are all swept under the rug when one makes a hasty comparison between the results from two different labs.
IMO the most important question is whether or not such a small amount of material is useful in a forensic context. There are several reasons to question whether or not it is. The 2013 review article by Meakin and Jamieson that I have previously cited is one source for information on low levels of DNA, and it mentions the problem that when an item of evidence is packaged the location of the DNA may be affected. Presumably this happens if the object tumbles around, coming into contact with the packaging and transferring the DNA to different locations on the object. The source of Amanda’s DNA on the blade may well be her DNA that was on the handle.
Dr. Schneps does not seem impressed with arguments based upon secondary or tertiary transfer. Nowhere in this passage does Dr. Schneps address the problem that Gubbiotti repackaged the knife. There was no reason whatsoever to do this, and I would have tossed the knife on the grounds that the packaged was opened alone, apart from all of its other problems. His clothing may have carried DNA from the flat to the station. I gave a citation some time ago in these threads which showed that DNA can be found on clothing that is neither from the wearer or his/her immediate family.
A major problem here may be that when DNA profiling was first introduced, large amounts of material were needed, a point that Dr. Gill made in a very recent interview. The introduction of PCR made it possible to test small samples, and the use of low template DNA requires even less material. As objects get smaller they are transferred more easily and in ways that are not always noticeable. Perhaps a simple analogy might help. An ordinary breeze is not strong enough to carry pebbles, but it is capable of blowing sand around.
I’d like to come back to the question of dedicated facilities because it is related to the question of aerosol DNA. Facilities working with low quantities of DNA often have special air handling needs, as I mentioned on my blog. If airborne contamination were impossible, as some PG-commenters seem to believe, then all the money that is spent on these facilities, and precautions such as pipet tips with aerosol barriers is wasted. BTW DNA may be detected several feet past where a person is speaking, which is further evidence of the existence of aerosol DNA. Dried blood is a more serious problem than wet blood from the point of view of aerosols.
An additional problem is what the SCC said about the test on 36I. They referred to it as “decisive.” How can it be decisive if the results are inculpatory, no matter which way the test turns out? A related problem is that Nencini turned aside valid requests from the defense, raising questions about his objectivity (and answering them).
Dr. Schneps does not address the paradox of DNA but no blood on the knife in this passage. The 2004 article by Peel and Gill makes me question more forcefully how this would even be possible. Nor does she address Stefanoni’s credibilitiy problems. In addition, the problem of laboratory contamination is far more extensive than the question of how many days elapsed since the last time a piece of equipment was used. For anyone to draw the inferences that Dr. Schneps does (that 36B is strengthened and that Vecchiotti was wrong) is completely unwarranted.
