When prisoners were dragged into the photo room at S-21, the brutal Khmer Rouge torture facility, photographer Nhem En could offer little solace.

His life depended on staying emotionless and shooting the mug shots of each terrified prisoner exactly how his bosses wanted.

“Technical accuracy was essential, because I knew that my life would be in danger, if I was careless in my job.”

En’s account of his time as a photographer in S-21 comes in a memoir due for release in the New Year.

In Nhem En: The Khmer Rouge’s Photographer at S-21, the 54-year-old writes how he joined the Khmer Rouge at age 9 and was later sent to China to train as a photographer. He returned to an empty Phnom Penh when he was 14 years old and was put to work in the torture facility.

More than 12,000 people, including many Khmer Rouge cadres and a handful of foreigners, were killed after being tortured at S-21 between 1975 and 1979 under the watch of prison boss Kaing Guek Eav, alias Duch. But En was aware of up to 400 staff at the facility – other cameramen included – also being killed, he wrote.

“They simply might have fallen asleep during their working hours.”

En himself was close to being murdered, he says in his book, over a negative he developed showing a blurred line across Khmer Rouge leader Pol Pot’s left eye.

It was later discovered that the defect wasn’t his fault, but he still spent three months in exile at a rabbit farm in Meanchey district as a consequence.

En said yesterday that his book, co-written by Dara Duong, a Khmer Rouge survivor, provided a personal perspective of a regime that killed at least 1.7 million people.

“This book is not about politics. It is my personal [experiences]. I want my memoir to give some history,” he said.

The authors plan a second book, detailing En’s later years as a photographer for Khmer Rouge guerrillas.

En lives in Anlong Veng, where he defected to the government in 1996. Earlier this year, he stood down from his position of deputy district governor and later joined the Cambodia National Rescue Party.