A senior citizen is much more likely to kill a bad guy because they know they can not beat him in a physical fight. The senior citizen was attacked and he defended himself. The good guy lived and the bad guy died.
It should also be noted that the bad guy was a serial offender. Do you think he would have let his victim live after attacking him? If the victim lived he could identify his attacker and send him away for a long time.
Beware of old men carrying weapons, as a rule they are kind, courteous and respectful and know how to kill you. They have probably been shooting for many many many years. They do not wish to be hurt or die. They will kill you.
There it is.
Did you miss the irony?