a smaller knife would have been compatible with all of the wounds as well as the imprint

(Massei, 170) seems to disagree (although I could be misreading it), but I welcome any counter-arguments.

The argument there is pretty weak: Massei and Cristiani simply find it hard to believe that a single knife could have caused such different-looking wounds. Not much more than an argument from personal incredulity; they don't support it with any detailed arguments or expert opinions indicating incompatibility of a smaller knife. In fact, they proceed to argue at length that Item 36 itself is compatible with all the wounds, by disputing the defense arguments that it is incompatible with some of them. (For counterarguments on this, see pp. 36-51 of Knox's appeal document, and pp. 20-23 of Sollecito's. Since you cited the original page number of Massei, I'm guessing you can read Italian. If not, I can provide translations. Briefly, the important things to note, besides the object-level defense arguments themselves, are that prosecution expert Bacci "disavowed" his earlier judgement of compatibility, and that civil-party expert Liviero wasn't even aware of the defense experts' counterarguments and hadn't considered them.)

The closest thing to evidence for (the knife being bleached) is that a police officer claimed to have smelled bleach upon opening the drawer that the knife was in. (That doesn't distinguish the knife in question from the others, needless to say.)

I disagree: "Let me state beforehand that it was extremely clean" (Massei, 99)

Such a statement strikes me as extremely weak evidence, likely tainted by hindsight among other things. Bleaching is the kind of thing you establish with chemical tests, not someone's judgement of "looking clean".

The innocent explanation is that (Raffaele) had been told about the knife DNA result, and believed it.

I give the odds that he would tell such a lie if guilty as .1, and if innocent as .001; what odds do you give? Why would Raffaele believe the DNA result? He's more likely to believe it's not the murder weapon if he's innocent, and also less likely to lie if innocent.

Firstly, since we don't have the transcript of the interrogation, we don't know that it was a "lie". It could, for example, have been an exchange like this:

-- We found Meredith's DNA on a kitchen knife in your house!

-- Well, I guess she must have come to my house and pricked herself, then!

But in any case my probability that he would make up some story similar to this (or otherwise say something that would likely be reported as him making up such a story), given (1) innocence, (2) that he had been told about the DNA result, and (3) had demonstrated confusion about his memories elsewhere (e.g. suggesting at one point that Knox had gone out on the evening of the crime), is in the region of 50%. People tend to trust authorities, and defying the data is an advanced rationalist skill that cannot be counted on, especially in the face of shouting policemen. From what I understand, it is relatively easy to get people to make things up in stressful interrogation situations.

I think if she's innocent, reacting to the knife like that is about .05 likely, and if she's guilty, about .005 likely. What odds do you give? You wouldn't be more likely to react strongly to an otherwise-irrelevant event if you knew it was going to practically end your life?

(I assume you meant to reverse those numbers.) Let's make sure we agree on what event we're referring to. My assumption was that you were talking about Amanda's distressed reaction when an officer opened up a drawer containing knives in her cottage (i.e. not Raffaele's apartment -- nothing to do with Item 36). I don't understand why this event would have any life-ending import. I'm not aware of any similar story regarding Item 36, the closest thing being an expression of concern about it to her parents at one point. Very plausible innocent explanations for both include, in the first case, distress at Meredith's demise primed by the sight of knives, and in the second, the knowledge that she had handled the knife while cooking.

(I predict that if you took 100 young females and put them into a situation where they knew a friend or roommate of theirs had been killed with a knife by an intruder, and then showed them a drawer full of knives, the number of those who would react with visible emotion would be well into the double digits.)

My reasoning: suppose a chef grabs a knife in cooking position ten times and nose-picking position once. Suppose further DNA is only found in one spot. It's probably ten times more likely that the DNA is found in cooking position, and that his unhygienic habit will remain undetected (aside from the giant nasal scars).

This seems to be an argument against the proposition that Amanda used the knife for cooking more than for stabbing. But that seems unlikely to be sound, since even if it was used for stabbing at one point, it had presumably been used for cooking a fair amount before. It was a kitchen knife after all, and Amanda had spent a lot of time at Raffaele's apartment.

In any case, this kind of inference seems like it is subject to tremendous uncertainty. How much difference is there between cooking positions and stabbing positions anyway? Surely there are any number of ways to do both. Why 10:1 or 2:1, instead of 3:2 or 10:9? As a matter of fact, I'm curious in general: what sort of evidence of guilt would have a likelihood ratio below 2 for you?

But in this situation "knowing the knife isn't a murder weapon" doesn't come close to being necessary for innocence.

I disagree: not necessary, but probable, by a factor of >10 IMHO.

Can you explain this more? Why should an innocent person have knowledge of what the murder weapon was or wasn't? If she were innocent, why should she, under the circumstances she was in at the moment, with the information she had, doubt Raffaele's guilt any more strongly than she indicated in the diary excerpt (already fairly strong, IMO)?

I'm more concerned by: “This could have happened: Raffaele [killed Meredith] and then, having come back home, pressed my fingerprints — I was asleep — onto the knife", from London Times

That is almost certainly just a mistranslation of the passage I quoted above (in its original form). See here and here (#8). (Admittedly, I haven't found a "neutral" source explicitly recognizing this mistake, but it is extremely plausible a priori, not surprising at all that the media wouldn't bother to correct it, and moreover no one can produce photographic evidence of the second version, unlike the first. Even the guilters use the version I quoted.)