Well if he'd had his camera going, this would be made clearly obvious. So why are the police against camera? (To be fair, many of them aren't. But I'm talking about the ones that are. Which to me means they've got something to hide, if nothing more than a feeling that their privacy is being invaded, and where they were dominant, now they are supervised.)
Unfortunately there have been enough instances where the police are obviously lying and at fault that I prefer objective evidence that doesn't require that I theorize to fill in the pieces. E.g., there are power stains on someone's hands, but how do you know that he got them when you think he did? A reasonable hypothesis is that he got them struggling to take the officer's gun, but it this actually what happened? And if he was 150 feet away when he was shot, was he fleeing? A camera would remove uncertainties...provided it was secured against tampering. (Yeah, OK, nothing's certain. It could reduce uncertainties quite significantly.)
And why is anyone against having a camera to prevent this kind of uncertainty?