The problem with your logic, cgnavarro, is that you would have to wait until the enemy's bullet has left the gun before you could predict that he would shoot at you. You would have to wait until the enemy's knife has pierced your skin before you could predict that he would stab you. In fact, since we all know that many gun shot, stabbing, and bludgeoning wounds are not fatal, you'd have to wait until the nerves are obliterated or the arteries are severed to know with metaphysical certainty that he means to do you LETHAL injury before you would be justified in returning LETHAL force upon him.
You are justified, in most sane jurisdictions that I know of, in visitting deadly force upon a person if you can invoke the reasonable person standard. In otherwords, you can show that your thought processes AT THAT MOMENT were such that a metaphorical reasonable person would agree with the decision to hit, stab, shoot, etc. the person.
If you have to wait for that iron clad guarantee that you're about to be attacked, you're already dead, and that iron cladding is going on your casket. I could and would claim that I believed that at any moment, that purse snatcher was going to wheel around, aim a gun at me, and since the criminal at that moment was still in my presence, it's reasonable, and so I am justified in ending that threat with a .357MAG between the shoulderblades. If the criminals falls down and stays down before I can realign for a second shot, cool, I get to conserv ammo in case he has an accomplice. If he's still up, well, then, the threat hasn't ended, has it?
That is, if I'm operating on enough of my rational mind, or the training has taken over. But, if I'm operating instinctually out of fear, I might just be pulling the trigger until I hear click instead of boom, and that too would be reasonable.
In the end, the incident was one of the criminal's making, not the self-defense shooter. If he didn't want to get shot in the back, there was an easy way for him to accomplish that... don't be a criminal that day.