I think a possible solution to that is to have the body cameras rigged so that the cams will activate when the cam is outside of the vehicle the officer is riding/driving in, seeing as if the dash cam is already on?
As an aside and not in direct response to your post, I think that in a war zone, just pointing a finger at an armed combatant who is at a distance looking for threats can and does have deadly consequences. For me, every encounter a cop has to meet is a potential "mini-war zone" in and of itself, and If I were in a cop's shoes, it's how I would approach an encounter that warranted such suspicious alertness.
Now I'm not alluding to the idea that the victim of the shooting should'a known better than to do what he did if in fact he wasn't armed, or if he was carrying but didn't have handgun in hand, but damn if I'd put myself into the same "apparent" predicament he was in. That's just asking to get shot, unintentionally or otherwise.
From what I saw in the vid, I'd say if it was an accidental shooting, the victim was partly responsible for getting shot according to how he made himself look like he was a direct threat.