He overpaid his debt (spoilers)

I mean the guy he killed might had killed others. But he definitely was a crook. Crooks can be family men too, still they must know that getting killed is an "occupational" hazard.

So if 30k of his ill begotten gains are given for his executioners' son surgery. That's ironic. But I wouldn't consider that unconscionable. As far as karmic justice is concerned, the executioner may had some small debt to the widow, but certainly not his life. He could have continue to carry for her daughter or even repay it eventually. But he chose to die because he was too conscientious of a person for his own good.