1. If you are a witness, call the police immediately.
2. If you are a victim, go to the police as soon as humanly possible. If you are in the hospital, tell them you want to see an officer. Do not wash your clothing or bodily parts. These may be evidence. Above all, do not delay. I know this is tough, but you can stop this vermin.
3. If you are a friend, urge, urge, URGE them to go to the police and provide them with valuable evidence.