In early 1999, in a village in northwest Cambodia, an elderly man introduced himself to a journalist.
He was Hong Pen, he said, a former teacher from the capital, Phnom Penh. He spoke good English and was wearing the T-shirt of an American aid organisation.
But the journalist recognised his face - it matched a photograph he had carried with him for several months.
The picture was of Comrade Duch, the former head of Tuol Sleng prison.
There, during the four years of Khmer Rouge rule, 17,000 men, women and children were interrogated and tortured. Then they were killed, their bodies tossed into mass graves.
The chance meeting with the journalist led to Duch's detention.
Tomorrow he becomes the first of the surviving Khmer Rouge leaders to go on trial at Cambodia's UN-backed genocide court.