I don't usually weigh in on behalf of the shooter in these incidents, but it's pretty clear to me that in this case, the decendent and his partner went after what they thought would be a soft target.
They inflicted considerable injury on the old fellow, from which he might never recover.
Had he not gotten loose and gotten his weapon, what else might they have done to him?
I hate to say good for the old man, but in this case, that's what I think.
One less punk to prey on those they believe to be weak and easy targets.