Wow, I feel for the kid.
I guess at that age he wouldn't have been strong enough to pry the guy off his mother and hold him down. He did what he had to do. I hope he doesn't get pressed with any charges, it is homicide, but it also is defense.
At that age, I would have done the same thing, no other way to get the attacker off. <img src="/ubbthreads/images/graemlins/frown.gif" alt="" />