That’s a tough case to prosecute.
What nation was he committing espionage for?
Some other hackers including the Jester have speculated that Assange created WikiLeaks as a way to use the information he got from hacking in order to blackmail those he stole the information from. He may have been spying for himself, or maybe, working for someone like Soros as some have speculated. I think the blackmail idea has credibility although in his early emails and writings, it may just be ideological. His parents were communists and he has written often about wanting to take down the US.