This officer has been charged, and, I believe, will be convicted especially because of the video.
I feel bad for everyone concerned, but in my view, the reason we punish perps is not out of hatred for the perp, but to discourage others from committing the same crime. When enough cops go to jail for murder (or assault in lesser cases of police abuse), then cops will start to think twice before stepping over the line.
In this case, I'd bet all the dead man's wounds are in his back. It will be really hard, in light of the video, for the defense to make the case that the dead man was attacking the cop.
When I was stationed at Ft. Bragg, a soldier from the 82nd Airborne Division shot a Somali kid in the back with a 40mm buckshot round. His defense was that he felt threatened, but the kid's wounds were all in his back. The prosecution said, "You felt threatened by a 70 pound Somali kid who was running away from you?" Dude was found guilty. I'd bet this cop will be as well.