Warn your friends and family, but otherwise do nothing. It is very important that you wait until the case is resolved. Trying to tell this man's boss or his own family of this case is not the right thing to do. Innocence until PROVEN guilty - that is the foundation of our legal system. You might suspect this man of being guilty. He might very well be. But until it is PROVEN that he is, you must presume innocence. This applies to all crimes, including rape.
Do not go around saying that this man is guilty, even if you really feel that he is. If the evidence is strong enough, he'll be convicted. If he's not, then he won't be. The court system is not perfect, but it's the best system we have for now. In the case of rapists, it does let too many go free. But I would rather let 10 rapists go free, than put one innocent person in jail. That's the way it has to be. Again, it's not perfect. Rape is a horrible, horrible crime and currently, we could do more to investigate and prosecute offenders. But we can't just say "He's guilty! He's guilty" until it is proven in court.
Lenin once said that he would rather hang 100 innocent people than let a criminal go free. Do you agree with Lenin? Or do you favour the principles of the West, which argues that putting an innocent person in jail is pretty much the worst thing you can do?
I don't know if this guy you speak of is guilty or not guilty. I haven't seen the evidence, I haven't interviewed the suspects or the victims, I haven't heard the arguments. From what you have written, he sounds guilty, but I do not have the knowledge or the authority to make such announcements, and neither do you.
Just to clarify - rape is horrible crime. I am not saying that this man is innocent. I am just saying that I would not go around shouting "he's GUILTY, I tells ya, HE'S GUILTY", because not only does that 1) Prejudice the community against him BEFORE a crime has been proven in court and 2) It indicates that a judgement has already been made on your part, which is not the correct thing to do - the correct thing to do is to wait until the court case has been settled.