The prison had a staff of 1,720 people throughout the whole period. Of those, approximately 300 were office staff, internal workforce and interrogators. The other 1,400 were general workers, including people who grew food for the prison. Several of these workers were children taken from the prisoner families. The chief of the prison was Khang Khek Ieu (also known as Comrade Duch), a former mathematics teacher who worked closely with Khmer Rouge leader Pol Pot. Other leading figures of S-21 were Kim Vat aka Ho (deputy chief of S-21), Peng (chief of guards), Mam Nai aka Chan (chief of the Interrogation Unit), and Tang Sin Hean aka Pon (interrogator). Pon was the person who interrogated important people such as Keo Meas, Nay Sarann, Ho Nim, Tiv Ol, and Phok Chhay.