Hou Yuon was one of the first senior leaders to be purged. The Khmer Rouge originally reported that he had been killed in the final battles for Phnom Penh, but he was apparently executed in late 1975 or early 1976. In late 1975, numerous Cambodian intellectuals, professionals and students returned from overseas to support the revolution. These returnees were treated with suspicion and made to undergo reeducation, while some were sent straight to Tuol Sleng. In 1976, the center announced the start of the socialist revolution and ordered the elimination of class enemies. This resulted in the expulsion and execution of numerous people within the party and army who were deemed to be of the wrong class. In mid-1976 Ieng Thirith, minister of social affairs, inspected the northwestern zone. On her return to Phnom Penh she reported that the zone's cadres were deliberately disobeying orders from the center, blaming enemy agents who were trying to undermine the revolution. During 1976, troops formerly from the eastern zone demanded the right to marry without the party's approval. They were arrested and under interrogation implicated their commander who then implicated eastern zone cadres who were arrested and executed.