For the Cambodian people there would be no one coming over the hill to save them for years, (until Vietnam invaded and sent the Khmer rats scurrying back into the jungle). They were on their own against some of the worst humankind has to offer and in that disintegrated world Dith Pran (played brilliantly by Dr Haing S. Ngor), bereft of his western sponsors, is as powerless as any other Cambodian citizen to stop the hemorrhaging. He must forage for compassion, put out the lightest of feelers for spiritual connection and stay strong while those around him do their utmost to tear him down. The Khmer Rouge said they were starting over again with the year 0, and it only seems fitting. What other number would suffice to describe a world shorn of cultural touchstones and family ties, where history and education were dirty words, countless numbers were worked to death and heavily armed children were encouraged to pass snap judgements on people they didn't know. This was nihilism on an institutional level not seen since the Holocaust and Joffe bravely attempts to confront it by following Pran through a largely wordless hell.
It is a story that can only be told effectively through the use of the camera, where minute gestures or facial expressions can spell the difference between life and death, and Joffe seems to instinctively understand this. He doesn't pad out Pran's story with clumsy exposition. The dread is in the silence. Hearing is used only to ingest propaganda or to listen for predators. Speaking is prohibited. If you don't know how to observe your chances of survival are slim at best. So, like the people he's chronicling Joffe observes and we observe along with him and them and in the end we find that words come hard when trying to explain what happened and, more importantly, why and how. Only that it did and that if people hadn't kept their eyes open to the horror unfolding around them and remembered what they saw there's a chance no one on the outside would have ever known what really occurred.
Maybe that's the lesson of The Killing Fields: don't look away. Don't ever look away.