No, Wilson could have acted out of anger, making mistakes. That's not anything close to "insane". I believe Brown could have fought the cop through the car window, also a mistake, reactive self defense and not insane. What's insane is Brown charging at Wilson who had a gun drawn. It's much less likely that happened than Brown was giving up and getting down on the ground.
That was mentioned. That Wilson blew his fuse because Brown had put his hands on him, possibly punched him in the eye, possibly tried to grab his gun, and he got out of the car and shot Brown down. That's pretty much what the eyewitnesses have said happened. I'm not sure how the police are going to be able to prove something different. But experience tells me in these kinds of cases the police officer usually, not always, but usually walks.
I go all the way back to a case in Brooklyn where a cop was accused of killing an unarmed teenaged car thief by shooting him in the back. His
own partner testified against him and he still walked! [ . . . ]