This example can is mirrored over and over.
A couple of years ago here in Ireland a farmer found a Traveller on his land who he 'suspected' was about to rob him. He shot him in the leg, wounding him, beat him with a stick as he lay on the ground, went into his home and re-loaded and administered the coup-de-gráce, killing him.
Verdict - self-defence, punishment - none.
Jim Carroll