002/19-09-2007-ECCC-OCIJ ЮŲŠ / No: D427 buildings were also part of S-211817 and were located in a second outer perimeter, which was also protected by armed guards.1818 They included, for example, the houses for interrogators, execution sites and mass graves, messes, a “medical centre”, several offices and houses for Duch and a house for receiving prisoners.1819 418. At the beginning, executions were carried out either inside or near S-21.1820 On an unknown date between 1976 and mid-1977, Duch decided that prisoners would henceforth be executed in Choeng Ek.1821 However, even after Choeng Ek became the main execution site, some prisoners were still executed and buried within the confines of S-21or nearby.1822 Operation Organization and personnel 419. During the meeting of 15 August 1975, Son Sen appointed Nat as Chairman of S-21 and Secretary of its Committee1823 and Duch as Vice-Chairman in charge of the group of interrogators.1824 The detainees were brought to the S-21 interrogation unit from the Ta Kmao Psychiatry Hospital, which In Lorn alias Nat, with his Division 703 staff, used as a detention centre.1825 In March 1976, Nat was appointed to a position at the General Staff and Duch replaced him as Chairman of S-21 and Secretary of the S-21 Committee.1826 Duch maintained Khim Vat alias Hor in the position of deputy in charge of the daily management of S-21. Nun Huy alias Huy Sre was the third member of the S-21 Committee; he was also in charge of S24.1827 As chairman, Duch was in charge of choosing personnel1828 and provided training, particularly political training, for the staff.1829 Duch also taught S-21 personnel interrogation methods and techniques for executing detainees.1830 420. Duch ran S-21 on the basis of a hierarchy and set up a sytem for transmitting information at all levels, thereby ensuring that his orders were immediately and precisely followed.1831 S-21 was divided into several units:1832 the Interrogation Unit;1833 the Documentation Unit (responsible for registering and maintining records);1834 the Defence Unit, which had two subunits, the Guard Unit (responsible for guarding the detainees within the prison complex) and the Special Unit. The Special Unit had several duties: it received people who were sent to S21 or, in some cases, made arrests or transferred prisoners; it intervened in emergencies and escorted prisoners to Choeng Ek and carried out executions.1835 421. S-21 was both a political and military establishment. Duch states that S-21 was an independent military regiment under the direct control of the General Staff as regards Extraordinary Chambers in the Courts of Cambodia, National Road 4, Choam Chao, Dangkao Phnom Penh Mailing address: P.O. Box 71, Phnom Penh; Tel: +855(0)23 218914 Fax: +855(0) 23 218941. 109