This is why the Castle Doctrine is bullshit. Who the fuck cares if the kid opened the door? That’s not justification enough to shoot him.
Castle Doctrine only applies to someone entering your home against your will. So if the kid was shot outside the front door then Castle Doctrine doesn’t apply. If he was inside the home, then under Castle Doctrine it’s reasonable to assume the stranger invading your home doesn’t have your best interests in mind and that you don’t have a duty to flee from them but instead may defend your home as an extension of self defense.
Usually the line is drawn at the threshold - if they’re outside the threshold then Castle Doctrine doesn’t apply. So if he was literally shot for knocking at the door/ringing the doorbell then Castle Doctrine wouldn’t apply., but if he was shot while trespassing inside the home…