There were double withdrawals though. And at least Mt Gox should have a record of by who..

You could probably get a pretty good idea with careful examination of the blockchain, but you'd need Mt Gox's withdrawal records to be sure.. but the exact same amount withdrawn to the same address more than once, combined with hash padding issues seems like a good place to start.. Cross referenced with Mt Gox withdrawal records and their KYC records and it seems like you should be able to knock on someone's door and ask some good questions..