Haha, that is really funny because the hacker seems to be complete idiot to me. I am not sure how he ended with such bullshit decision of not accepting the offer. I can not imagine someone just leaving the millions of dollars just like that.
Now to identiy the hacker himself they are offering bounty of millions of dollars. According to the source mtnioned in the OP we can clearly read that anyone who identify it will get:
That is a whopping $1.85 million just to identify. Obviously this not gonna be easy and will be riddle for many but those who were close to this case from beginning must have kept an eye on the initial hacker who supported the case. Now its all about the "back tracing" and also keeping keen eye on the movement of any funds during this transition from their wallets.