The killers modelled themselves on their favourite characters from Hollywood and recreated scenes they found particularly exciting. Anwar Congo, who had started off by bludgeoning his victims to death, switched to garrotting. "I watched gangster films where they always kill with wire, it's faster with that, you could deal with more of them," he recalled calmly.
He acknowledged personally slaughtering hundreds of the "enemy", without any remorse, and the death squad he led played a full part in the massacres in which half a million people, including women, children and the elderly, lost their lives – often in the most brutal way. Others disappeared, never to be seen by their families again.
That was almost half a century ago, and now many in Indonesia – a state seen in the West as an example of a developing democracy with a strongly emerging economy – say the time has come to shine a light into the dark corners of a past that have been hidden away from accounts of contemporary history.
There has been no legal or moral resolution to the savagery that unfolded during that period, no process of "truth and reconciliation" such as that which took place in South Africa, nor any drive to bring the murderers to justice, as took place in Rwanda. Instead, the likes of Congo continue to live openly, feted by figures in authority, and feared by the families of those they slaughtered.
Now the murderers are starring in an extraordinary film about their exploits. The Act of Killing, made by the British director Joshua Oppenheimer, with Werner Herzog as a producer, has already received huge approbation at international festivals; it is due to open to the wider public in the near future amid anxiety in Indonesia about international reaction.
Anwar Congo and his friends were small-time thugs who dealt in bootleg cinema tickets before a secret cabal in the army used them to wipe out the country's communist party, the PKI, as well as socialists and trade unionists, a vast number of them ethnic Chinese. This laid the ground for the replacement of an increasingly weak President Sukarno, a leader of the Non-Aligned Movement whom the West accused of cosying up to China, with Major-General Suharto, the choice of the US and UK.
The Cold War was raging and America, paranoid about the "domino" theory of successive states in south-east Asia tumbling into Marxism, was about to embark on the Vietnam war. The role played by the CIA in organising the coup, with the help of the military and fundamentalist Muslims, was revealed soon afterwards. However, it was not until 1997 that The Independent, in an article by Paul Lashmar and James Oliver, exposed the part played in the plot by the British government, which had sent troops to Malaya in response to a perceived threat by Indonesia.
Denis Healey, defence secretary at the time of the coup, told the newspaper that he did not have any "personal knowledge" of clandestine UK action, but said that he "would certainly have supported it".
Harold Wilson's Labour government was in possession of accounts, from the embassy in Jakarta, of what was really going on. One appalled diplomat wrote: "PKI men and women are being executed in very large numbers. Some are given a knife and invited to kill themselves. Most refuse and are told to turn around and are shot in the back."
The film has reopened old wounds in Indonesia. It comes soon after a report by the country's National Commission on Human Rights has demanded that the government take steps to address what took place in those lethal months in 1965 and 1966, start a programme of reconciliation, and prosecute those still alive who were responsible.
But there are voices decrying attempts to investigate. The Communists were not only victims, it has been pointed out; they too persecuted their enemies. Nusron Wahid, the head of the Ansor Youth Movement of the religious Nahdlatul Ulama (NU), asked: "Many NU members were killed at the time many of the PKI were killed. Do we really want to dig that all up again? Do we need another war?"
Harry Tjan Silalahi, the chairman of the Indonesian Catholic Students Association, which had also clashed with the Communists, was adamant: "I cannot see how there can be a settlement soon. It will take a brave president to do it, and the passing of another generation."
The current President, Susilo Bambang Yudhoyono, a former general, was the guest of the Queen during a state visit earlier this month, part of a drive by the UK to cultivate links with Indonesia, which is seen as a lucrative market and an influential regional player. President Yudhoyono, who has high ratings in opinion polls, may issue a state apology for what happened, but there are no plans at present to launch a public inquiry, as some civic groups have demanded. One worry among officials is that attempts to charge religious activists who were involved in the killings may be exploited by Islamists to create dissent. Indonesia is trying to recover from a more recent trauma, the bombing in Bali 10 years ago, in which 202 people, locals and foreign visitors, were killed.
Anwar Congo and his gang did not have any particular political or religious reason for their campaign against the Communists; their main grouse was the PKI's advocacy of a boycott of American "imperialist" films, threatening lucrative ticket sales and their aspirational lifestyle of "Rolex and Relax". The boycott call was also an insult, they held, to their heroes, such as John Wayne and James Dean.
They proudly describe themselves as "gangsters" or "preman" in Indonesian, their monicker partly based on a "translation" by one of their supporters, a former vice-president of the country, Jusuf Kalla, who has stated that "freeman" is the English for "preman" and so gangsters are "freemen".
At the end, declared Adi Zulkadry, a member of one of the hit squads: "We were allowed to do it. The proof is we murdered people and we were allowed to do it. War crimes are defined by the winners. I am a winner, so I can make my own definition. Not everything true should be made public. Even God has secrets."
It is unsurprising that in such a climate it is the victims rather than the perpetrators who remain afraid. The pogrom came to Bali later than the other islands, then took place in a frenzied burst. Alice Leu Cheng's family were only allowed to revert to their original name after the departure in 1998 of Suharto, who had decreed that all Chinese names should be Indonesianised. Along with the disappeared identity, the fate of her father was a matter which was also not mentioned in public.
"He was just a good member of the trade union, maybe he was militant, but he was never violent," insisted the 55-year-old teacher. "But they came to our home at night and took him away. We found his body in a field eight days later, he had been stabbed many times. Of course no one was ever arrested, although we had a good idea who did it.
"There has been a lot of publicity about the bombing here in Bali. There is a memorial, people were put on trial. But they just pretend to forget what happened here in the Sixties.
"We don't want revenge, my parents and I just want the facts. The tourists who come here should know what happened in this beautiful place in the past. We are a grown-up nation, we should be able to cope with it."