You cannot shoot someone who is no longer a threat. If a person is running away and still has a weapon you are generally justified in shooting him in the back. This is because when a person has a weapon and they are running they could just be running for cover and not simply escaping. That’s why if you shoot a guy that’s running away from you but deeper into the house, you can shoot, while if they exit your door and you shoot then outside the house it’s very different things even if they are both shot in the back while running away from your position. In this case the man had just fired a weapon at an officer while running, meaning That he wasn’t escaping, he was still escalating the use of force.