He actually took less than three seconds to kill the dog. I re-watched the clip several times last night and need to make a correction. I said Hall panicked, but I was wrong. Only a cold, efficient and concentrated person could've killed this dog the way Hall did. One...two... then boom. The dog was dead.
Hall started moving his body into position (sideways and backward to left) to shoot the dog the very instant the dog exited the car. He got his bead, stepped forward and the dog is lying dead on the ground.
The last few times I watched the clip, I turned the sound off. (I simply couldn't stand listening again.)