It seems to be that victims in such situations spend so much time ignoring or manipulating each other, that it's often not necessary for the dictators to enforce suffering one-on-one anymore. Why for example, were some decisions made about the son, when the group travelling might have been able to trade him hand-to-hand on the journey?
Nevertheless, Cambodia today is still ruled by "good" Khmer Rouge, and it's likely that essential, culturally specific experiences of being Cambodian, if you want to understand how 2 million people let themselves be gradually starved to death, can't be expressed explicitely by this former minister of roads or many of the world's observers.