The courts have ruled that YOU determine when a person is no longer a threat to you. Look it up. Once the shooting starts, you don't stop shooting an armed or dangerous suspect until, in your mind, he's not a threat. If I go to shoot Johnny Dirtbag and, if I think he's a threat, I will not hesitate to put one in his head, step over him and do whatever I need to do. Keep in mind, not all head shots are fatal but most of them are incapacitating. There are numerous reports of felons being shot in the head only to have the bullets go under the skin and slide around the outer bone of the skull. Most people who get shot in the head and don't die from the penetration of the bullet end up out of action with a very serious concussion. More than likely you're probably going to kill the suspect but not every time. So a head shot has too many variables in it but your survival doesn't: Take out the bad guys as effectively as you can.