A third development was Sihanouk's own belief that he had been targeted by United States intelligence agencies for replacement by a more pro-Western leader. Evidence to support this suspicion came to light in 1959 when the government discovered a plot to overthrow Sihanouk. The conspiracy, often known as the "Bangkok Plot", involved several Khmer leaders suspected of American connections. Among them were Sam Sary, a leader of right-wing Khmer Serei troops in South Vietnam; Son Ngoc Thanh, the early nationalist leader once exiled into Thailand; and Dap Chhuon, the military governor of Siem Reap Province. Another alleged plot involved Dap Chuon's establishment of a "free" state that would have included Siem Reap Province and Kampong Thum (Kampong Thom) Province and the southern areas of Laos that were controlled by the rightist Laotian prince, Boun Oum.