[LINK] Amanda Knox exonerated

Isn't this also confounded by the fact that judges and juries like to go easy on women, so that women who do commit murder are less likely to be convicted? It may be that measures of what fraction of women are convicted of murder are not the same as what fraction of women are actually murderers.

Update on both living with the victim and being female and the small probability is bigger but... still small, since the still relatively low probability of a roommate murdering is penalized substantially by being female

Low compared to what? For someone murdered at home in the dead of night, the dominant probabilities are that either the murderer was invited in or lived there. Roommates merit investigation. If the evidence clears spouses/lovers and close family, then the probability of it being a roommate goes up considerably. Being female is not going to lower the probability enough to eschew a thorough investigation.

What saves Amanda Knox in this case isn't being female, but rather evidence that someone else committed the crime, as well as the lack of physical evidence of her involvement or any paper trail pointing to a conspiracy.

extent that pretty girls do not have differing patterns of murdering roommates from other women, you're making the exact same mistake

That's an interesting claim. Do you have a source for "pretty girls are less likely to murder than girls who aren't pretty?"

By looking at the genderless conditional probability ('somebody'), you're implying that women like Knox might have male-like murder levels, which is obviously wrong.

No, male-like murder levels would be higher than genderless murder levels. And, if I understand correctly, most of the excess male murder rate involves gang-related violence, which in this case was pretty clearly not involved.

Anyway, I agree that if you are doing pure Bayesian inference you have to condition on all kinds of available evidence, including gender, race, social class, nationality, etc. But we can't expect courts to consider this kind of evidence, for good reasons (avoid creating self-fulfilling prophecies and avoid incentivizing crime within certain demographics).

Let's analyze the problem using Bayes Net terminology. Let A={suspect=Knox's demographic profile}, B={suspect lives with victim} and C={suspect guilty}. Then your claim is that the net is structured as A->B->C, or that the demographic evidence is conditionally independent of guilt given co-habitation.

No.

My claim is that the net is structured as A->C<-B; both A and B affect the likelihood of guilt, and in particular A substantially reduces the likelihood of guilt as James_Miller points out (Note that I'm not saying B is irrelevant, obviously this is wrong).

I agree.

There's all sorts of complicated details that are completely missing from the US coverage of the trials, which make the prosecution's position much more understandable. Perhaps the prosecution did not have sufficient evidence, but neither did the prosecution come up with some batshit insane theory out of the blue for no reason when they had everything explained with Guede.

Komponisto is Italian and translated documents from the prosecution for the benefit of the community.

The prosecutor claimed that from the number of stab wounds, it was unlikely that a single person could have inflicted them all. However, the number of stab wounds was by no means an outlier among murders known to have a single perpetrator (I do not have detailed statistics on this subject, but merely from my limited experience with case studies on the subject I have encountered quite a few cases which involved many more stab wounds from a single perpetrator.) Considering the pervasive incompetence their forensics teams demonstrated over the course of the case, I would assign very little weight to this.

The prosecution also presented pieces of "evidence" such as Knox placing extremely short phone calls to Kercher, too short to transmit any message. This and many other points raised by the prosecution fit the pattern of behavior that seems unusual, and so is presented as evidence for suspicion of murder, despite the fact that the behavior doesn't make more sense if we suppose she was involved in the murder.

If Knox had a murder likelihood of 1/1000 after conditioning on the evidence that Kercher had been murdered, but before accounting for other evidence, and she's then observed to have engaged in unusual actions with a 1/1000 probability, it makes no difference towards her likelihood as a culprit if they're not actions which are more likely in the event that she's actually guilty. We can come up with post-hoc explanations for why the unusual things might be related to involvement in the murder, and this kind of reasoning appears to have constituted a large part of the prosecution's case, but if we don't have any prior reason to suppose that guilt of murder is associated with such behaviors, then these explanations will tend only to be rationalizations of preexisting suspicion.