Ieng Sary: Leading figure of the Khmer Rouge who later stood trial for crimes against humanity

Sary is assisted by guards during hispre-trial hearing in Phnom Penh in 2008 (Reuters)

Ieng Sary or "Brother No 3", was the co-founder, with his brother-in-law Pol Pot – "Brother No 1" – of the communist Khmer Rouge. They ruled Cambodia with unremitting cruelty and were responsible during the 1970s for the deaths in the "killing fields" of an estimated 1.7 to 2.2 million people. Decades later he was one of a clutch of former Khmer Rouge leaders to be put on trial by a UN-backed tribunal for crimes against humanity, war crimes and genocide.

The regime's bloody reign of terror, between 1975 and 1979, saw about a quarter of the population disappear; they were simply executed or died through starvation, disease, overwork or torture as Pol Pot tried to turn Cambodia, then Democratic Kampuchea, into their version of an agrarian communist state by evicting people from cities to work in labour camps in the countryside producing rice and creating irrigation systems.

Sary served as deputy prime minister and foreign minister. He denied any wrong-doing, claiming that Pol Pot "was the sole and supreme architect of the party's line, strategy and tactics". He also blamed Nuon Chea, "Brother No 2," the Khmer Rouge's chief ideologue, who is currently on trial alongside Khieu Samphan, a former nominal head of state. "Nuon Chea implemented all Pol Pot's decisions to torture and execute those who expressed opposite opinions and those they hated, like intellectuals," Sary said, claiming that he was excluded from Pol Pot's secret committee which decided policy on executions.

Sary's wife, the former social affairs minister Ieng Thirith, had also been charged but was deemed unfit to stand trial last year, suffering from a degenerative mental illness. Although they were first brought to trial in 2011, the process has been plagued by allegations of corruption and interference from the government, which has a number of former Khmer Rouge fighters in its ranks and as political allies.

Prosecutors claimed that Sary was responsible for persuading hundreds of Cambodian intellectuals to return home from overseas; arrested, tortured and put in re-education camps, most of them were later executed. Researchers discovered documents showing that Sary was indeed in the inner sanctum and that he "repeatedly and publicly encouraged, and also facilitated, arrests and executions". One cable sent in 1978 indicated that he had full knowledge of the bloody purges. It read: "We are continuing to wipe out remaining [internal enemies] gradually, no matter if they are opposed to our revolution overtly or covertly."

In 1984 Laurence Picq, a Frenchwoman who had married a Khmer Rouge activist but later defected, said Sary "saw conspiracies and traitors everywhere. He led denunciation sessions that would turn into collective hysteria. Young wives denounced their husbands without evidence, children denounced their parents. All children of workers were revisionists and members of the Soviet KGB. Anyone who had ever smoked an American cigarette was CIA. Any person with nostalgia for a café crème on the Boulevard St-Michel belonged to the French secret service. Anyone with Chinese blood was an agent of Beijing or Taiwan."

Born Kim Trang in 1925 in Vietnam to a Cambodian father and Chinese mother, Sary moved to Cambodia, then a protectorate of France, in 1942. He met Pol Pot in the mid-1940s when they were classmates at Phnom Penh's élite Lycée Sisowath. He changed his name and became part of the pro-independence Democratic Party, helping to organise anti-colonial demonstrations in the late 1940s.

In the early 1950s he was one of many young Cambodians who won scholarships to study in Paris. Studying political science, he met Pol Pot again and joined the French Communist Party. A natural orator, he dominated the Marxist circle he co-founded. In France he also met his future wife, and fellow radical, Khieu Thirith.

Having had his scholarship withdrawn due to his political activities, Sary stayed in France before returning to Cambodia in 1957. He and his wife lived for a short time with Pol Pot, who had married Thirith's sister, and the four became teachers in Phnom Penh, joining the newly-founded Cambodian Communist party's central committee in 1960. In 1963, when suspected communists were being arrested, he and Pol Pot fled to the jungle to start a guerrilla movement, the Khmer Rouge.

In 1970, as the movement gained momentum and war raged in neighbouring Vietnam, Sary went to Hanoi to establish a radio station for the revolutionary movement. In 1971 he moved to Beijing as a special emissary of the government-in-exile, his role to co-ordinate the Cambodian resistance after US-backed General Lon Nol ousted the ruling Prince Norodom Sihanouk.

When the Khmer Rouge took power in April 1975 – Year Zero – following bitter fighting against Lon Nol with Sihanouk's support, Pol Pot was named prime minister and Ieng Sary his deputy responsible for foreign affairs.

In August 1979, the Khmer Rouge was ousted by a Vietnam-led resistance and the regime's top brass fled to the Thai border, waging an insurgency until 1996. Eight months later Sary and Pol Pot were sentenced to death in absentia by the court of a Hanoi-installed government which was made up of former Khmer Rouge defectors like Hun Sen, the current prime minister who has ruled almost unopposed for 20 years. Pol Pot died in 1998, having never faced justice.

During the guerrilla conflict Sary was in charge of Khmer Rouge finances and was believed to have amassed a huge personal fortune, embezzling millions of dollars. Perhaps with suspicion falling upon him from Pol Pot, he struck a peace deal with Hun Sen. Days later he led a mutiny of thousands of Khmer Rouge fighters to join the government, which was a prelude to the movement's collapse in 1999.

Hun Sen initiated a royal amnesty for Sary, granting him a diplomatic passport. Until his arrest in 2007 he lived a comfortable life, dividing his time between his luxurious villa in Phnom Penh and his home in Pailin, a former Khmer Rouge stronghold in north-western Cambodia.

Kim Trang (Ieng Sary), politician; born Tra Vinh, Vietnam 24 October 1925; married 1951 Ieng Thirith (one son); died Phnom Penh, Cambodia 14 March 2013.