My girlfriend was d and all i want is revenge... what should i do?

more than 4 years ago my girlfriend was d... she met up with this dude during a break up and he tried to move in on her she refused and in an uncontrollable fury he d her. she was afraid to tell for months. when i finally found out we went to the prosecutor and police. this s bag's father is a cop in our town and now he is a cop in a town over. All of the authorities said to bad not enough evidence etc. etc. i tried to tel everyone but still he got hired as a cop. he was in 2 different departments and i set up meetings and told both chiefs. both said get some help and get over it. It is disgusting. All i want to do is cut off his . honestly.... i will not feel right until he gets what he deserves. I know you will think maybe she lied...i hoped that for awhile. but after being diagnosed with ptsd from her psychiatrist, trying to kill herself and a million other symptoms i can safely say i am sure this really happened. what can i do to ruin his life?