This is something that happens in quite a few action movies: The hero and the bad guy fight it out, and when the hero wins, he spares the life of the bad guy. (Or even saves him!) Shortly afterwards, the bad guy dies by accident, or gets killed by another bad guy, or just anybody who's not the hero. He gets punished but the good guy doesn't have blood on his hands.
The strange thing about this is that the film is essentially less friendly and forgiving than the hero it's supposed to be about. Why does the bad guy get killed by the plot even though the good guy disapproves of that? This is probably so that the audience can feel merciful and still see the bad guy get punished. Also, the hero's conscience will be nicely clean.
A less extreme version of this is that the good guy spares the bad guy, but the bad guy then attacks again and promptly gets killed by the hero.
On a related note, I'd really like to see a movie once where, at the end, the good guy goes to prison for harming innocent bystanders and causing enormous property damage.