Before fleeing his northern stronghold, Khmer Rouge leader Pol Pot orders the killing of his defense chief Son Sen and 11 of Sen's family members.

Khmer Rouge is the name that was popularly given to members of the Communist Party of Kampuchea (CPK), and by extension to Democratic Kampuchea, which ruled the country between 1975 and 1979. The name was coined in the 1960s by Norodom Sihanouk to describe his country's heterogeneous, communist-led dissidents, with whom he allied after the 1970 Cambodian coup d'état.

Pol Pot was a Cambodian politician, revolutionary, and dictator who ruled the communist state of Democratic Kampuchea from 1975 until his overthrow in 1979. During his reign, his administration oversaw mass atrocities and he is widely believed to be one of the most brutal despots in modern world history. Ideologically a Maoist and Khmer ethnonationalist, Pot was a leader of Cambodia's Communist movement, known as the Khmer Rouge, from 1963 to 1997. He served as General Secretary of the Communist Party of Kampuchea from 1963 to 1981, during which Cambodia was converted into a one-party state. Between 1975 and 1979, the Khmer Rouge perpetrated the Cambodian genocide, in which an estimated 1.5–2 million people died—approximately one-quarter of the country's pre-genocide population. In December 1978, Vietnam invaded Cambodia to remove the Khmer Rouge from power. Within two weeks Vietnamese forces occupied most of the country, ending the genocide and establishing a new Cambodian government, with the Khmer Rouge restricted to the rural hinterlands in the western part of the country.

Son Sen, alias Comrade Khieu (សមមិត្តខៀវ) or "Brother Number 89", was a Cambodian Communist politician and soldier. A member of the Central Committee of the Communist Party of Kampuchea/Party of Democratic Kampuchea, the Khmer Rouge, from 1974 to 1992, Sen oversaw the Party's security apparatus, including the Santebal secret police and the notorious security prison S-21 at Tuol Sleng.