1) There is no reason to assume that the victims DNA would be limited to the blade. I think even you do not believe that this is a real argument. Blood would have got on to the handle and need to have been cleaned.
2) As I think you accept there is an argument that Knox's DNA is not proof BYRD that she wielded the knife. If there is a likely alternative explanation for Knox's DNA on the knife it was the responsibility of Stefanoni to present that to the court. All I argue is that a reasonable assessment of the evidence does not result in a conclusion that the most likely explanation for Knox's DNA on the knife was that it was deposited at the time of the murder but that it was deposited post cleaning (if it was the murder weapon).
3) I completely accept as said above you believe that separate from the knife there is evidence that Knox is guilty. It is clear there is no way you will deviate from this position. I have clear criteria which if met would convince me of Knox's guilt. I have no fixed issue on people, I do have strong feelings that the prosecution science in this case is pseudo-science. I would remain of this opinion even if I was an eyewitness to the crime.
4) You really do not want to get into another argument with me about the properties of cells and whether shed epithelials are more adherent than leucocytes or have higher levels of DNA. Just take my word for it that blood is far more likely to deposit DNA on a surface than epithelials from hands, by a huge order of magnitude. Most of the epithelial layer is apoptosed keratinocytes with no analysable DNA whilst macrophages are highly adherent cells with intact DNA. We know from the electropherograms the MK DNA was NOT 200 pg, but around 40 pg. In my opinion not on the blade at all but in laboratory contamination; but that is another issue. You will not believe me when I say that this assay was so incompetently performed as to be meaningless, I know that I would never accept this result if done in my lab, (actually I would be very angry if this had happened in my lab). So we just have to agree to differ on this.
(...)
I'll leave aside other arguments for a moment and focus now only on one of the topics in your post.
The first thing I notice is you completely shun point 2. What you answer to point 2. looks like a mess made of arguments of physical kind disconnected from the point and arguments of law mashed together, really cobbled together avoiding the point. You also mention Stefanoni so maybe you meant to use the argument in a particularly indirect way, trying to transform it from a matter of evidence into a legal argument against Stefanoni and this is really a dreadful meshing and patching together. It seems to me you haven’t really understood the point, so I’ll try to explain again more clearly: Knox’s DNA is a non-relevant finding,
in comparison to the finding of Meredith’s DNA on the blade. It means the probative implications of the two findings are not of the same magnitude, they have different magnitudes.
The finding of Meredith’s DNA is hugely stronger, as probative implications, on all logical levels, compared to the finding of Knox’s DNA. I mean
at all levels, including the drawing of scenarios, deductions and conclusions from them. You shall always derive scenarios, speculations, deductions and explanations from the first findings to the second (explain the second on the basis of the first) and never the other way around.
You may not make deductions about the origin of Meredith’s DNA based on the presence of Knox’s DNA, because you can’t dismiss something intrinsically more relevant on the basis of something logically less relevant: this would be legally unacceptable.
Meredith’s DNA would be an extremely significant finding even without any Knox’s DNA, because there is no plausible justification for Kercher’s DNA on an object in a drawer inside Sollecito’s apartment, whereas Knox’s DNA on the handle itself would have rather poor relevance (except for trace "I" which has some more relevance because it shows to be likely from Knox’s blood rather than from epithelial cells – Knox’s blood being another topic which you fail to consider; note that it was not known at the time).
Setting aside for a moment the point about Knox’s blood, I repeat the logical concept: the DNA from Meredith is certainly of high relevance, whereas the finding of Knox’s DNA may be non-relevant. This must be taken together with another point: it’s a point that you miss when you say “Stefanoni should have said” that “Knox was not BRD wielding the knife”. Not only the point is legally wrong because you must always explain an irrelevant finding based on a relevant one and never the other way around, but it is wrong also because, under a legal point of view, it is intrinsically irrelevant whether Knox was wielding the knife or not.
Not only the
assumption that you would like to use is the non-relevant one, but also the
circumstance that you apparently wish to demonstrate is a
non-relevant factual circumstance in legal terms.
Put it simply, the fact that Knox was wielding the knife is not what needs to be proven beyond reasonable doubt. This is only a circumstance, a detail which adds specificity to the scenario, and won’t change Knox’s responsibility, while the relevant piece of circumstantial evidence is Meredith’s DNA found on a weapon in Sollecito’s apartment. Who was wielding the knife is an object of conjecture, after the evidence is found; the probative value doesn’t come from there and it is not the circumstance that needs to be proven.
That said, additionally, we should mention again the fact that Knox’s blood was found on the scene, and her DNA was found in the insertion of the blade in the handle, where epithelial cells hardly get. Thus, any reasoning based on the assumption that Knox’s DNA are epithelial cells has intrinsically just a value of speculation, there is actually no need to assume they are epithelial cells bearing in mind that Knox’s
blood could be an equally valid explanation. This is merely an additional point, unnecessary from a logical viewpoint, but if you like it, it also exists.
Let’s come to the last aspect of your answer to #2: you mention Stefanoni rather than just considering the probative aspect of the findings.
It seems you want to use the argument not just to make a point about DNA, but rather in an indirect way, apparently you try to use it to attack Stefanoni, using it together with some statement she said, rather than to discuss the evidence directly. In other words you try not to make an argument of science but to build a legal argument against Stefanoni, and this is a part where you mess up with legal arguments. Your argument doesn’t stand because you have no ground to attack Stefanoni’s “ethics” or reliability as a witness on this; Stefanoni didn’t say anything wrong, she expressed an opinion – considerations about Knox’s DNA on the blade having a legal value of conjectures – only making valid points and fully respecting the principles of law.