Though it may be a bit of a stretch to say that Mark was in any way ever directly involved with them. He seems to imply that he was not in his SR timeline piece. Why do you think an unknown intern may have been part of any scheme? That's news to me.
He admitted he had been losing BTCs since sometime in 2011 from MtGox's hot wallet via the allegedly "
Transaction Malleability".
Since WizSec's last report was published, the theory Mt. Gox's bitcoins were lost over a period of years beginning as early has 2011 has gained some traction. If so, it suggests your insider must have been active over a long period of time. From what I understand, there were only ever 30 people including contractors working there. If the insider was not Mark, then s/he should be easy to indentify. Who was this sneak?