Your last line says it all, jls. Had the guy obeyed orders and just sat there in his car as directed he would still be alive today. BUT, there is no excuse for shooting someone in the back if all he is doing is running.
You can not use DF against an unarmed fleeing person to prevent his escape. This Officer was wrong in his actions, first by shooting the guy while he was running away, and then his dropping of the taser near the victim is proof he tried to cover his own ass.
I would expect a quick indictment of this cop and a conviction for this murder. I feel for the cop's family, but what he did was criminal and he deserves to be in jail for a long time. That man did nothing to merit being shot. You're correct, had he followed the Officer's instructions to remain in his vehicle, he would still be alive today. But his actions in running away should not have resulted in his death, at most he should have been chased, taken down and cuffed. That guy was no sprinter, he wasn't getting away, he should have been caught within fifty yards by any cop in reasonable shape. Plus, there were other cops responding, they could have easily blocked him with their vehicles from getting away.
As for the other cop at the scene, unless there is clear, convincing evidence that he actually saw the other cop dropping the taser near the victim, he should not face any criminal charges.