The thread i found of it back then was from 2009, and it was supposedly a training video.
if you notice as he put down the rifle, he pulls out a handgun from behind is back when the officer in the rear yells "GUN"
Also, notice the camera man isn't taking cover, and i think more importantly the approaching officer's gun doesn't recoil. Now if you suggest that the officer in the back shot him, he wouldn't of fallen backwards (i think). He would of fallen backwards if the officer in front shot him.
I have found a few website about this event and calling it training but none of them are listing departments or anything like that.