A violent gangster-vigilante is forced to judge his own actions and be sentenced by his own laws.

I think you’ve made it TOO vague. Now a reader can’t tell what your film is about at all. What is the goal, and what are the stakes? The “murdered an undercover cop” tactic worked, because from that we can extrapolate that the stakes are his freedom or life (depending on how viscously the other cops pursue his capture), and that for some of the movie at least he’s going to be trying to dodge the police force’s efforts. But we’re still unclear as to what your vigilante wants … what is he doing?