Hypothetically speaking say you get this guy. Find him and kill him. First off who's to say you even killed the right guy. Assuming It was in fact him that you killed what happens if they find out this guy was completely set up by the LAPD in the first place therefore you just murdered an innocent guy.
If in fact it was dead or alive how many more civilian superhero commandos do you think it would take randomly killing people who somewhat resemble this guy before all hell breaks loose. This is not the wild west anymore, you can not go around and personally become judge, jury and executioner.