As difficult as this scenario is, I cannot fault the officer for his actions. He sees a guy holding an AR at an active killer event, and responds appropriately.
"Hurley fatally shot the gunman, Ronald Troyke, 59, with his own handgun after Troyke ambushed and killed Arvada Police Officer Gordon Beesley with a shotgun, officials have said. Troyke had also retrieved an AR-15 rifle from a truck. Hurley had apparently picked up the rifle and was holding it when he was shot, authorities said."
It has been said before and will be said again, do NOT have a gun in your hand when the police arrive, and they will be arriving sooner than you might realize. "Hands up, don't shoot!", while based on a false narrative, still has merit when the cops roll up.