He tried to brute force password hack with Chelsea Manning. Worked with her directly -- to me, that's pretty much a clear and cut case of "hacking". Regardless of the attempt was successful or not.
If we're going to base his guilt off of the similarity in his actions to Manning then remember that Manning was pardoned. It would be pretty piss poor precedence to ignore that and charge assange in a different light.
Let's not forget that Manning's sentence was commuted by Obama (which technically isn't a pardon) in part because Assange stated on twitter that if Obama granted Chelsea clemency then he'd submit himself to US extradition. Obama called his bluff and Assange reneged on his offer.
Manning was convicted. Pardons are not a statement of guilt or non-guilt but a political tool. Assange might yet be pardoned, but I'd be surprised.