It is the second of circumstances that seems appropriate in this case. I tend to believe the officer did wrong if he shot to kill a ‘distant’ suspect’. However, the second of circumstances would appear as a possibility in that ‘violent’ serious felony on a police officer had been committed. More than one shot can be arguable.
Allegedly Brown was facing the officer with his hands up. The question is did the officer think Brown was going to charge him, especially since they had just had a scuffle in the patrol car and a round was fired. Tough decision under the circumstances with your adrenalin running sky high from the struggle inside the car with someone trying to take your gun away.