Well, Julian either let it slip or he is exploiting what others have said previously. I don't know his reputation or his political M.O. well enough to really have a hard opinion one way or the other but I'm leaning towards an accidental, maybe semi-accidental disclosure because Assange is a very serious person. I think he would be genuinely devastated to know that someone was murdered because of a leak earmarked for Wikileaks.

Credibility seems extremely important to Julian and his mission so I can't accept the argument that this is just gamemanship even though he is an exceptional gamer. He is walking a fine line trying to say a source has been murdered yet holding steadfast to the position of wikileaks never to reveal its sources. Regardless, he has insisted repeatedly that the source was not a state actor . (Though, he never clarified whether all possible intermediaries were likewise not associated with a government.)

And finally, this is evidence that the emails were a result of a leak, not a hack. In the absence of an FBI forensic inspection of D.N.C.'s computers it represents the greater weight of the evidence. At best the self serving hired gun report by D.N.C.'s expert serves as a check, not a checkmate and that should have been acknowledged by authorities and the news media.