If the police are involved, then a case number should be provided...
1. I do not trust the police.
2. Nobody forced anyone to use MtGox! The issue here is the one between MtGox and the hacker...
Maybe you should go: "Oh I was really stupid. I used a fucking weak password, and I put all my money in one place, I must be a genius!"
If fraud was committed, it's irrelevant. Fraud was committed. Legal proceedings should proceed and parties should be judged as so.
So basically by your analysis it's irrelevant whether or not MtGox stole money, because users decided to sign up?