What "appropriate group"? The central bank of Bitcoin? The Central Bitcoin Intelligence Agency?
You have no idea which addresses belong to MtGox. It doesn't strike you as utter contemptible to just start blocking addresses because you think they belong to MtGox? Forget laws, on what ethical or moral authority do you have the right to arrest the wealth on another person?
As I suggested at the beginning of the thread, I would suggest a group of people, reasonably respected in the community, be set up to judge the evidence. To proceed fairly they would have to weigh the evidence for particular addresses. These addresses can always be unlocked if an owner can submit proof of proper ownership by other than Mt. Gox.
There are quite a few discussions on the web where the evidence looks reasonably compelling that there are large blocks of bitcoin which previously belonged to Mt. Gox and haven't been spent since. I don't believe it is accurate to qualify this evidence as "no idea".
There is another alternative to viewing this as arresting the wealth of anyone. It could be viewed as the miners simply refusing to take part in what they judge to be an unethical transaction. I don't think there is anything wrong with miners deciding they don't want to support what may be a massive fraud or theft.