I spoke (politely) with the guy who ran the organization that publicly went after my friend — I think he genuinely considered what he was doing to be legally safe, and I also think he was convinced my friend was guilty. His livelihood is now in tatters.
No you don't need that. The OTHER party needs to have bulletproof evidence, because the accuser is innocent until proven guilty.
If something is true, then you should never ever ever be afraid to say the truth. Go public with your true accusations, and then force the other side to sue you.
Because if you are telling the truth, then you will win, because the other side can't have evidence that you are lying, because the evidence doesn't exist.
It is basically impossible to get in legal trouble for libel, if you know that what you are saying is true.
You are innocent of libel and slander until proven guilt.
So if someone is raped, they are pretty safe calling the attacker a rapist, they just can't call them a convicted rapist until a court has decided that.