The haunting snapshots and false confessions churned out of Phnom Penh’s infamous S-21 prison were explored yesterday at the Khmer Rouge tribunal, which also tackled potential conflicts of interest within the courtroom.

With the heavy click of the camera shutter, Nhem En – a mere teenager in 1976 – produced thousands of black-and-white portraits that now line the rooms of the Tuol Sleng Genocide Museum.

Now in his mid-50s, En testified yesterday for the first time at the Khmer Rouge tribunal in Case 002 against Nuon Chea and Khieu Samphan, detailing the events that led him to become a photographer at the prison where more than 12,000 people perished.

En served as a messenger before he was sent to China for six months in early 1976 to learn photography skills, before returning to stand behind the lens at S-21.

“We had no choice but to do what was assigned to us,” he said.

“I knew many of the interrogators and the murderers . . . Many of them, later on, were also killed.”

En has detailed his experiences before, but while a defense team request to admit his autobiography – Nhem En’s Personal Memoir at S-21 – into evidence will soon be decided upon by the trial chamber, the book has courted controversy in the past.

In March last year, En was forbidden to sell his book at Tuol Sleng out of fears that it presented him as a victim, when in fact he was a security centre employee. He had sought permission to sell it alongside S-21 survivors such as Chum Mey, who returned to finish his testimony yesterday prior to En’s appearance.

In his cross-examination, Nuon Chea defence lawyer Victor Koppe held on to doubts that Mey had actually been imprisoned at the prison.

“It’s a question I have to ask, so please don’t be upset. We have doubts as to you being really in S-21, so were you really an S-21 prisoner?” he said.

The prosecution team objected, saying that there was “absolutely no basis” for the “humiliating” question, in light of evidence confirming his detention, including the name “Chum Mey” listed on S-21 records.

Mey later gave an impassioned speech on his suffering, building on yesterday’s court session where he testified that he had fabricated names under pain of torture, and said he wished to apologise to anyone with those names who had been implicated and arrested as a result of his false confession.

Earlier in the day, Khieu Samphan defender Kong Sam Onn signalled he would not question four of the case’s upcoming witnesses in order to dodge a potential conflict of interest, as he had represented them as duty counsel in the court’s Case 001 against former S-21 director Kaing Guek Eav, better known as Duch.

But whether Khieu Samphan, at the request of the judges, would formally waive his right to appeal on the grounds of his lawyer’s recusal was not resolved.

Nhem En will continue his testimony today.