If the bitcoins were in fact stolen, then you had no legal expectation of keeping them no matter what price you bought them at.  In fact, you're lucky you are getting a roll-back rather than losing your investment completely.  If a cop found you in possession of a stolen vehicle, it won't matter that you paid for it.  They'll take it from you and give it back to the rightful owner.  It would then be your responsibility to go after the person who sold it to you.

Having said that, we have no way to validate the official story as it stands.  I do not necessarily trust or distrust MtGox.  But they need to provide confirmation of their own statements of fact.  If the police are involved, then a case number should be provided.  Perhaps a scanned copy of a police report?  I'd have much more trust in MtGox if I knew the owner has reported this to the police, if for no other reason than the fact that filing a false police report is typically a felony.