The idea sounds like glorified RDM, but just read it all out.
Vigilantes can kill people with only 1000 crime, but it should only be active when there are no cops.
If they kill the person with over 1000 crime it could put them in jail for 30-180 second depending on the level.
If they have a bounty then it's normal.
Just a random idea. Sound like a random new job.