The person whose account was hacked (if it was one person) is entitled to their Bitcoins and it's MtGox's responsibility to provide that to him. Kevin did nothing wrong making a large purchase of bitcoins, but now that he KNOWs the bitcoins were stolen, he's possessing stolen property, which can be a felony. The fact that MtGox's account was hacked makes all the difference here, as it makes the bitcoins which were traded stolen property.
This.
Even if the bitcoins were MtGox's to begin with, the trades should be reversed. Kevin did a pretty smart thing in jumping in there to grab those BTC, But the release of the DB shows that it was a hack, whether from an insider or from someone in it for the lulz, and the person (or persons) whose BTC those were should get them back.