Norng Chanphal, who was nine years old when he and his family were arrested by the Khmer Rouge and sent to the infamous Tuol Sleng prison, wept before judges at a UN-backed tribunal Thursday as he recounted the torture his mother underwent as an inmate.

Tuol Sleng’s administrator was Kaing Kek Iev, better known as Duch, who is on trial at the Khmer Rouge tribunal for war crimes, crimes against humanity, torture and murder.

When Norng Chanpal first arrived at the prison, known the Khmer Rouge as S-21, with his mother and younger brother, he watched as prison staff put his mother before a camera and yanked her hair back, he recalled, at times weeping during his testimony.

He was separated from his mother, but he could see her standing at the barred window of a room on the second floor of the facility. She looked at him but would say nothing, he said.

Norng Chanpal was alive and in hiding when Vietnamese forces invaded Phnom Penh and ousted the Khmer

Rouge, liberating the prison where prosecutors say Duch sent 12,380 people to their deaths, following tortured confessions of acts against the ultra-Maoist regime.

As he fled the prison, Norng Chanpal saw bloodied corpses of inmates, he said, but he never again saw his mother.