You can’t kill murder. You can’t get revenge on evil. You can only begin to fight such things by not doing them.
Murder gnaws at the soul. Whoever did it will reveal themselves, sooner or later. No killer behaves normally over time.
When I go talk to the family and friends of a murder suspect, somebody I know is guilty, and I tell them the person they love is a killer, guess what they all say? “That’s not the person I know.”