It looked to me as if the police officer was in a position of either getting run over by a car or trying to stop the car by shooting at the driver. Even if the driver was trying to just push the cop over, it appears that the cop could've easily have been run over by the positioning of the officer in front of the car as the driver kept driving.
I'd say that it was a justified shooting . . . the officer could've been injured, the guy was given plenty of chances to get out of the car, there was a gun pointed toward him . . .