It might be that father and son and the 3rd party were trying to detain the jogger by holding him at gunpoint if necessary. They probably were far out of line doing this but may have not had any intent to kill him. When the jogger attacked his assailant and grabbed the gun I would imagine at that time the man holding the gun became quite fearful the firearm would be wrested from him and turned against him. The white man had put himself in a terrible position and might very well have felt he was faced with the life threatening situation of being shot with his own gun. Who knows what they were thinking. I can understand the black jogger's fear when confronted by a gun wielding stranger. He would have understood that he couldn't outrun a load of shot. His attempt to disarm may have seemed his only option. And the gun wielder may have thought his only hope was to do whatever it took to maintain possession of the weapon. The white folks involved used terrible judgement but it is highly possible they had no intent to kill anyone. If the black man was truly innocent of any criminal doings he likely thought his only hope was to obtain a weapon and went for the nearest one available.
Good analysis, and the one I have adopted as well. This would be a case of what's called "an imperfect defense of self-defense." When one is found guilty in that case, they usually get convicted of manslaughter, not murder. Imperfect defenses of self-defense are those that don't fully meet the standard for a perfect claim of self-defense, because the defender didn't come to the situation with completely clean hands, i.e., he was to some degree in the wrong as he appeared on the scene. An example of imperfect self defense would be walking up to someone and maliciously pushing him down, followed by the other party drawing a knife and charging at you, followed by you drawing your gun and shooting him down.
