Regardless of the threat of legal action, something should have been done. Even showing your face from 100 feet away and yelling will likely scare the attacker away. If the risk of being caught is high enough, he'll bolt. This is what's wrong with the world, people as good neighbors aren't willing to take matters into their own hands, to help each other. I guarantee you that if the situation was reversed and these guys' daughters or wives were being brutally raped in public they would want someone to intervene and not wait around for the cops to show. You don't need "training" to know that someone needs help. It's pure selfish cowardice.