I don't know the exact details on that. Whether low-copy or high-copy or everywhere-copy, why was Meredith's DNA found on the knife tip? I don't understand how Meredith's DNA could just magically appear on that knife. If it was the low-copy DNA or low-density DNA or whatever it's called, I would assume that if it was not reliable, they would not have been able to read whose DNA it was. As in, DNA from unidentified female or something like that. Yet it matched it with Meredith's DNA. And there is, IMO, no possibility of transfer/contamination as that knife was found in a totally separate location from Meredith's body and it was completely removed from the whole crime scene.
The scientific community does not accept low copy DNA as valid. The evidence was examined in the same lab along with other evidence of MK. It could easily become contaminated with other evidence in the lab. Moreover, there is a greater chance of false positives - more testing should have been done on that sample to confirm the result. Why doesn't the prosecution do another test? I suspect if the random female DNA turns out to be a technician, the prosecution's case is all but over.
WIth LC DNA they have to blow up the sample and whatever technique they use increases the chances that the result could go wrong. The prosecution did not use the most valid testing to do LC testing, they used an inferior method. Also it is not reproducible bc I think whatever technique they used destroyed the sample. That gave no opportunity for the defense or anyone else to confirm the result.
If that knife was the murder weapon you would not have to rely on the testing on one itself bitsy piece of that knife. MK's DNA would have been all over that knife. The fact that it was not increases the possibility that that test on that very small sample was just a false positive or was contamined,
Indeed, they should have found dna all over that knife, not just low copy but regular dna too. that is just common sense. If you are stabbed 46 times w an object your DNA is going to be all over that object.
And that is not the only problem with that knife. Why is not it blood DNA? There is no blood on that knife. How could you stab someone and not leave any traces of blood? MK's blood DNA would be all over that knife.
And if that is not enough, it also does not match the wounds. If the DNA was blood or if it matched the wounds maybe it would be more convincing but it does not. Or if other parts of the knife also tested positive.
Relying on LC DNA raises an extremely dangerous precedent. It would mean that the state can rely on DNA testing, say it is positive, then give the defense no opportunity to confirm the state's results because it was destroyed. That raises serious civil liberties issues, that is why low copy DNA is not considered admissible bc it just has too many problems with it.
Like I said, if there was low copy DNA all over that knife - and it was blood - there would be a more convincing case. The prosecution asked for more testing hoping they would find more and if they did that would be convincing. But they did not and I think they know that no higher court is going to uphold a verdict based on unreliable DNA evidence because of the horrible precedent it sets. Remember this case is not just about AK. If the SC and the European court of justice allow unreliable low copy DNA here they have to let it in in all cases. That would set Italy apart as one of the few(only?) country that allows unreliable scientific techniques to buttress convictions. It would sorta be like admitting lie detectors as evidence even though the scientific community believes them unreliable in all cases. No court is going to want to set that precedent, at least with the LC technique used by the prosecution here - and the absence or evidence that it was blood or that the murder weapon was a clear match.