I was just watching a movie, Training Day, (Edit: Spoiler - read no further if you'd like to not have the plot spoiled) where a good police officer is applying for a position on a narcotics unit, but he quickly finds himself in a position where his boss (leader of the unit) is requiring him to go along with a murder, and when he refuses, he's threatened with false testimony by multiple officers, and then the boss orders him killed by some criminals.
He ends up getting out alive, and then he's sitting on a bus with a loaded gun, wondering what to do next. He knows that the boss is in this operation with top people all across the government, and if he goes to the police, the feds, anyone, he'll be in great danger of being killed.
The one option that might possibly lead to him and his family surviving is to find and kill his boss, before his boss sends someone else to kill him.
That made me really curious, if we considered this to be a real life situation, lets say he finds his boss and kills him without imminent threat. Could he claim indirect fear for his life and possibly succeed in a self defense ruling?