The main difference between north and south of our border is that in the US once somebody has intruded your home, you the rules change
Not so.
Here, if you shoot someone and he stays down, you can't walk up to him and put one behind his ear just to be sure. Well, you can, but it stands a good chance of being called "murder". If he's out of the fight, it's over.
And most places to require that if they choose to run away, let them.