My girlfreind was d by her step brother 2 years ago should i go after him?

2 years ago my gf who i didnt know at the time was d by her brother in law. Her biological father which pardon my language but is whipped didnt even do anything and even paid for the pos lawyer to get him off with only community service and a restraining order. which btw the guy was 20 at the time my gf was 14. Earlier this weekend i was with her in her dads hometown(she tried to keep a relationship with him even after all this) and her step mother planned her son who d my girlfreind to come to the house where all of us were staying while i was away. Thank god i got back earlier than expected bad thing is i didnt recognize him because i have seen a recent picture and my gf didnt tell me till he was leaving which seeing him again obviously upset my gf very badly and is now suffering very bad because again her father stuck up for him because he wasnt suppose to be within a certain number of feet from her, but he didnt do anything again, suprise suprise, but question is im wanting to go and find him a long and kick the **** out of him yet everyone is telling me not to and that karma will come back to him *blah blah blah* but obviously he isnt afraid to go around her again since he just did (cept when im around as they planned it out cuz he hauled *** out soon as i got back). should i go after him or what should i do.