That's the difference between the legal concept and the regular one. You're a lawbreaker when you break the law; you're guilty when a court procedure agrees.
I don't know how in the US, but in Europe it is illegal to write publicly "Joe Average, a murderer", if the person had no trial, yet. Regardless of the widely available proofs.
After the fact - once the jury decided you are innocent - it is extremely hard to get your good name back.
Nope. The beauty of free speech is that it's only illegal if it's either untrue or you cant prove it (which are in essence the same thing in the eyes of the law) :)