Mach, the problem is that so much of what is described is what one sees in poorly run laboratories. One keeps a laboratory note book, one records contemporaneously what one does (for a good example of what happens if you fail to keep contemporaneous records read Strange Case of Dr Jekyll and Mr Hyde. Stevenson RL, Longman Green & Co. London 1886) Stefanoni obviously had not. There were clearly no SOPs in place. Appropriate controls were not run. When I was doing my PhD, the head of the department took my first draft of my first paper flipped through to the references pointed out I had spelt someones name wrong and said if I couldn't spell a name right how could he believe that the rest was accurate. He was right in the point he was making. One gets good results by paying attention to the details. There is no excuse for such a crappy report. If i was the director of the laboratory and one of my staff produced a report with such obvious holes in there would have been a long and serious talk, if the omissions were actual and not in the report, that discussion would have made it clear there would be no future in my lab. these errors are just dreadful! like seeing a surgeon spit on the scalpel and polish it on his shirt sleeve before cutting into you.
This is your opinion about the Polizia Scientifica report. I don't subscribe to it, I don't think that is a crappy work at all. I also don't consider it a laboratory work, and not as a report produced by one individual. I think it is also an unfounded assertion to say that operational procedures were not in place. Yet, I am not going to argue about your opinion. I will put it on a shelf. The point is elsewhere.
This is a murder case. There is a judge, and the focus of judgement is the defendant alone (and this is true even more when there is an inquisitorial principle in the system). Not the quality of the investigation, not the professionalism of this or that expert or witness or party, not even the quality of a piece of evidence: just the defendant alone. It's no zero sum game: the defendant does not become innocent if the detectives are unprofessional or the forensics are not good and not even if the prosecution is sloppy. Guilt or innocence of the defendant can only be asssessed by a judge directly and independently from all these external elements.
Second, this is a murder trial means it is about an overall system of evidence; it not a trial about DNA, nor about forensic evidence. It is only about evidence as a whole. And DNA, in this case, is an unnecessary element. Even if the forensics had been completely sloppy and had provided no DNA evidence at all, had I been the judge I would have convicted anyway. I would find them guilty beyond reasonable doubt with no need of DNA at all.
Yet, DNA here is not a "crappy" result at all. The bra clasp and the knife are valid results and good evidence simply because they fulfill the intrinsic property of good pieces of evidence: there is no likely explanation for them. The myth og "contamination" is in fact a conspiracy theory and thus is worth nothing.
And DNA findings on the knife are also part of a contiguous system. The victim's blood on the knife, for example, is not just backed by the DNA result, but also by the defendant's own admission that the knife came into contact with the victim. There was also the defendant admission that the victim's DNA might be found on the cleaning rags, there was Knox's admission in prison saying she was worried by the knife, there was Knox's DNA on the handle and on the blade at the handle insertion and there was her own blood on the tap where the murderer washed him/herself together with the victim's blood. Knox's DNA on handle, Sollecito's double and repeated admission, Knox's admission, Knox's DNA on blade, Knox's blood: this is a contiguous pattern of elements. In Italian legalese we say
conducenti, they are "conductive". The knife is also an incredible match to the bed sheet imprint.
All this is what makes the knife a piece of circumstantial evidence.
