Believe me when I say shooting a person is harder than you think!! You have to have the right mind set to pull the trigger and live with the consequences of your actions especially if it results in a death.
That being said some people couldnt give a shit who or what they shoot at.
The cop just needed to be a better shot. He did fire back, but missed with every shot(notice he shoots out the killers side window and all over the floor). If he just got one hit.... poor soul.