A depressing morning when I came face to face with the banality of evil.

In 1975, the Tuol Svay Pray High School was taken over by the Khmer Rouge and turned into the notorious prison, interrogation centre and torture camp known as S-21.

Between 1975 and 1978 more than 17,000 held at S-21 were taken to the killing fields outside Phnom Penh and executed. Many were bludegoened to death to save bullets.

The Khmer Rouge photographed the inmates as they arrived and the confused, scared and resigned faces of those whose death was assured line the walls of the prison, which is now a museum.

The horrors endured by those penned into the tiny brick or wood cells are unimaginable....chained and shackled to the floor,....manacled to steel beds and tortured and electrocuted, beaten and raped before being driven to the Choeung Ek Killing Field for what must have seemed like a merciful execution.

It's a deeply chilling place.

Read more about the Cambodian genocide here.