Uniformed Officers have responsibilities to protect public safety and their own lives. Along with this responsibility comes certain legal protections, because of the danger which comes with their job responsibilities.
That car was about to flee onto the public streets. being driven by a panicked teen who had been drinking and getting high, and was out on another stolen car charge from days earlier. She was not going to drive safely through those streets. She had 4 other kids along for the ride. It might have ended much worse if she was able to get away from that alley. JMO
I am not a lawyer, but I believe the danger has to be immediate to justify lethal force. The suspicion that someone may drive recklessly at some time in the future is a poor justification for homicide.