Inside the mystery of how Mark Karpelès and his Mt. Gox company lost almost $500 million in cybercurrency.
We don't know for sure, do we? but I believe that the last news were that the Russian guy who got arrested for money laundering had something to do with it. I'm still not sure If he is affiliated with BTC-E but If he is, he definitely did it well by hacking an exchange and creating his own in order to hide his traces and It definitely worked because funds are nowhere to find and something as big as 500$ million can't simply disappear.
Creating his own cryptocurrency exchange to hide his traces?Is it possible?
This requires tremendous amounts or work and investments,and still it`s very easy to reveal that
this "exchange platform" is fake.I think it`s possible for 500 million btc to disappear.If they are distributed across lots of offline wallets/cold storage and the hacker owns the private keys.
To answer OPs question,i would say nobody.The biggest bitcoin heist in history will happen in the future.