Historically having only 1 in 3 dying is a pretty good survival rate for communism
The only injustice was he probably went lights-out before he even knew what happened.
If there was REAL justice in the world, the clueless academic would've endured the whole S21 treatment, including the beatings, torture, interrogations and being forced to drink his own piss... protesting the whole time that there MUST be some mistake...... and refusing probably to the final bitter end to believe this was what his cherished Communism really could lead to.....
His two companions (journalists Elizabeth Becker and Richard Dudman) who survived the attack have no idea why he was killed or why they weren't, and summed up the seeming random murder of the regime's most faithful outside proponent as: "It didn't make sense, but
nothing made sense, it was madness, madness of the regime"
In essence, don't question it, violence against those inside its borders is just what communist states do, they kill their own citizens and anyone else they can get their mitts on as a matter of policy, asking them why they kill is like asking a bird why they lay eggs. The only language they know how to speak is MURDER because what's the only human equity that can be truly achieved for all but death?
Three days later, the Vietnamese, fed up with his border raiding and shit-talking, invaded and deposed Pol Pot's government.