Why do you feel he's "working for Russian interests" rather than their interests simply aligning? It's well known that Assange hated Hillary. It's far more likely he that if got material from Russia he published it in spite of it being from them rather than because they directed him to do so. He's on record in interviews as saying the following:
“Trump is a completely unpredictable phenomenon. You can’t predict what he would do in office. Hillary was overriding the Pentagon’s reluctance to overthrow Muammar Qaddafi. ... She has a long history of being a liberal war hawk, and we presume that she’s going to proceed.”
“Hillary Clinton is receiving constant updates about my personal situation; she has pushed for the prosecution of WikiLeaks. We do see her as more of a problem for freedom of the press generally.”
1) Wikileaks' reaction to the Panama Papers is a pretty strong indication Wikileaks is working for Russian interests.
2) The fact that Russia's propaganda arm employed Assange for years also kind of points in that direction.
3) The fact that Wikileaks basically never publishes any documents on Russian corruption despite it being one of the most corrupt states on Earth indicates that Wikileaks has chosen not to anger Russia.