It was allegedly initiated by the right-wing politicians Sam Sary and Son Ngoc Thanh, the regional Cambodian warlord and governor Dap Chhuon, and the governments of Thailand and South Vietnam with possible involvement of US intelligence services.
In early February 1959, Admiral Harry Felt, General Lawton Collins and Colonel Edward Lansdale all visited Chhuon's base in Siem Reap.
[3] Sihanouk's intelligence services discovered details of the plot and on February 21, 1959, they dispatched a battalion of troops to arrest Chhuon.
Sihanouk later alleged that Defence Minister Lon Nol had Chhuon shot to prevent him from being implicated in the coup.
Chhuon's brother Slat Peou, a member of Sihanouk's delegation at the United Nations and a friend of Matsui, was executed for treason.