Grinder,
Are you going from the book itself or my summary? I did not describe the experiments he proposed in detail. I see your point about the groove, but the groove is a red herring. Something that found itself in a groove would not be immune to the actions of detergent or bleach. The larger point is that experiments should have been done, as oppposed to offering assertions, which is what the prosecution did. This is what he said about the prosecution's contention that the knife was used for stabbing, not ordinary kitchen work: “However, this is dangerous speculation that is another example of confirmation bias—there is nothing in the scientific literature that remotely supports such an inference.” (p. 150)
From the English translation of the Massei report, p. 376, "It must be also emphasised that the presence of biological traces discovered on the handle of this knife, – and on which, regarding its attribution to Amanda, there was advanced no particular censure nor perplexity, – appears more likely to have been derived from her having held the knife to strike, rather than from having used it to cut some food.
"Remembering that this trace was found at the point in which the knife handle has a kind of upturn or rise [rialzo], after which the blade begins, with the knife positioned thus in a horizontal position with respect to the plane on which one is cutting [piano di appoggio], it appears somewhat unlikely to hypothesise that such a biological trace would have come to rest at the point indicated. Conversely, should the cutting implement be used for striking, and therefore moving it not horizontally, but with a certain inclination, it is quite probable for the hand holding the knife to undergo a sliding motion due to the violence required for the blow and, finishing up with a certain violence against said upturn, thereby leaving behind the biological trace."