After almost 8 months in Cambodia, I've finally visited the Tuol Sleng museum. My parents were in town and we decided to give it a go. The Tuol Sleng was a school turned to torture chambers by the Khmer Rouge regime. "Enemies of the revolution" were gathered, tortured, and almost all killed in this place. The bed where the prisoners were chained were left untouched, and there are a few rooms where you can actually see photos of prisoners (these were documented by the Khmer Rouge themselves).
In the end of our visit, my parents told me about a school in my hometown (Indonesia) used for the same purpose back in the cold war era. My dad recalled buses transporting people to another facility on the mountain, around 40 people transported daily and never to be seen again. The difference is "suspected communists" were the target. These victims were never mentioned in the history, I am guessing because they were "communists" therefore the value of their lives are of less significance.
To think of it, the value of each human life is different, depends on what one's political/ religious beliefs, nationality, race, etc is. Sad but true.