The Witness, who was a guard at S-21 in 1976 and later Head of The Special Unit, was responsible for arrests, guard management, coordinating transport of prisoners to S-21, and the transfer of prisoners from S-21 to Choeung Ek. He describes the location, authority structure and operations of S-21, including the inhumane living conditions to which the prisoners were subjected, and the use of torture during interrogations. He testifies to the execution techniques used at Choeung Ek.
The Witness describes a specific incident where a female detainee was raped. He also testifies to the interrogation, torture and execution of Vietnamese prisoners of war at S-21, as well as four Westerners, and numerous children.