The guy's past is almost meaningless legally unless the officers might have known that he is accused of having shot someone. That might tend to give them a "reasonable belief" that he might be violent. I doubt the officers knew any of that, if it is true.
It would make for an interesting conversation on whether a good person or a bad person was killed.
Of course the police video showing the guy getting out with the gun in his hand, not having his hands up as at least one witness claimed on a video.... makes a huge difference.