To clarify some questions that were raised here;
1)Knife is dangerous at 21 feet, you cannot stop a person from stabbing you if they are that close or closer
2)Police officers are trained to shoot at center mass, not to "kill" or to "wound"
3)Police officers are trained to shoot until the threat is gone, this is determined by the suspect, if they stop whatever they are doing that is a threat, the shooting stops
4)If you want to get a small idea of the feeling, go out and run a mile as fast as you can, ending 7 yards from a man size target, draw your weapon and fire and see how many times you hit the center
5)Unlike television, in our universe a half ounce of lead is not capable of stopping someone in their tracks, thus multiple rounds
6)When you are shot, unless it is through the brain, the heart, or a large bone such as the femur is shattered, you do not die, you go into shock and do not feel pain, particularly under stress, so you continue whatever it is you were doing
7)There are few experts around in the science of deadly force, the press does not have any on staff, anything the press releases is for ratings, not enlightenment