This is an easy one: justifiable homicide.
No, its stopping a criminal and defense. Not murder, justifiable or not.
Right -- that's what he said
Homicide is homicide -- sometimes justifiable. Not every homicide is a murder -- negligent homicide, justified homicide, etc.
This is a sad story, but if events took place as advertised (and considering the source, no reason to think otherwise!) it does sound like the shooting was justified. Sad for the robber's family (who knows, he might have been a nice kid etc, or if not, might one day have been a nice adult), and sad for the shooter, who probably will wonder at least occcasionally whether he did the absolute best thing. But justified nonetheless.
I like the way toivo put it above -- that no sane person would "gamble his life on the good intentions of the person who is robbing him at gunpoint" -- even if it somehow later comes out that the robber "would never had done it, really," or "didn't think it would go that far," or even (since the quoted account didn't say so) that the gun wasn't loaded. Yes, you can see the tip of the bullet in a typical revolver, but if someone waves a .38 at me, I bet I'll believe it's loaded until I'm well satisfied through personal inspection that it's not. (That's the downside to criminals of the four rules -- their guns are always loaded, too.)
timothy