Why was this sadistic SOB not executed?
I suspect that in Cambodia, as in Rwanda, there was an understanding that so many people had participated in killing that achieving peace could only be done by overlooking many of the atrocities. In Cambodia in particular, the Khmer Rouge had made a point of recruiting (in the countryside) then seizing (in the general population) children. They wanted to mold their young impressionable minds, but in the end they were no match for the NVA when they invaded in 1979.