Great background and setting drawing but not so great characters, beacuse the style feels like not in complete harmony with the rest of the image and story. Taking into account the type of story they are telling us, an undercooked or less detailed design would have worked better to me, leaving the only nice to see thing, the background, as the vanishing point for the viewer from the nightmare these people had to experience.
For those of you that want to know more about this historical event, i would recommend you this two documentaries; {S-21: the Khmer rougue killing machine} (2003) and {The missing picture} (2013),both directed by Rithy Panh.