Why kill the bad guy?
Why end his suffering by letting the truck fall on him? Surely it would have been fitting justice to let him live the rest of his life out locked up as a paraplegic? I mean once they saw that he was still alive they hit the jackpot in him getting his comeuppance, as it's very unlikely he'd be walking again after such a fall.
Also, about the first encounter with Walsh; would I be right in assuming that both Russell and his wife would have been safe and left alone had they simply stayed with their car?