In fairness, the guy's walking towards the cops with a knife, repeatedly saying 'Shoot me, shoot me, motherfucking shoot me' after they'd asked him several times to drop the knife.
Fuck knows what I'd do in that situation, but I'd be awfully wary of getting too close to him.
http://www.theguardian.com/world/2014/aug/21/police-release-video-of-kajieme-powell-shooting-in-st-louis
Includes a link to a video of the most recent shooting. It's horrible, though not close enough to be gory, but worth watching because it's beyond belief. Shooting to kill has become the first option. 12 seconds after arriving, they kill him.