To what extent could a person kill a criminal in self-defense without being convicted?

Basically you can't shoot a 'fleeing felon'. Also the felon has to be a real danger. A bare handed twelve year old probably isn't a threat. A fair sized 14 year old with a hammer could be if you're a small woman or in a wheelchair. If you're a small man and the felon is a large man, even if unarmed he could still kill or cripple you so shooting him is justified....of course that depends on the distance that you were when you fired. Closer than 12 feet is too close....if he's 20 feet away and not moving toward you...that's dicey. If he's 20 feet away and closing....we're in a gray zone. If you're an average sized man and the felon is small and armed with a tommy hatchet you might want him a bit closer than 15 feet..of course he could be just about to throw the hatchet at you....another gray zone. Armed, big and close...it's probably best to shoot. Small, unarmed and moving away...hold your fire. Shoot to kill...dead men tell no tales....just don't shoot the sucker in the back...that's a no-no!