I would be delighted to change this however you might see it evolving differently.
Miranda James can be a Private Investigator who has knowledge of a crime, but is set on taking out the perp on her own. He was arrested and charged, but got off on a technicality. She knows he is guilty but has no way to prove it, so she kills him. But can she get away with it?
You are a hard core veteran (police, CIA,FBI,NCIS) detective who arrested the guy and could not get the evidence to convict. You are assigned the case to find this douch bag's killer. But he had friends, and the Mob is out to get her because of her inside knowledge of the organisation. Will you help her or send her to prison where she will surely die due to inside Mob operatives?