In November 1965, the Indonesian Army warned a Dutch official in Sumatra that his locally-hired cook was about to be arrested on suspicion of being a communist.

The Dutchman stood his ground.

"Not till after lunch," said the man of principle.

"I've got a big party planned."

The Army obliged and the cook was arrested when he had finished his shift.

It is a pretty good summary of how the West viewed what was happening in Indonesia in 1965 and '66.

No big deal — a bit confusing, but the local communist party getting its comeuppance as part of a power struggle among the Indonesian generals who ran the place.

But these were Indonesia's darkest days, and what was happening would stain the nation for half a century.

Half a million suspects killed in months

Eye witnesses to the aftermath of the massacre tend to a monument at a mass grave in Central Java. ( AP: Dita Alangkara )

Echoes of 1965 are still heard on the streets of Jakarta today — an anti-communist and anti-Chinese hysteria that surfaces periodically, like during last year's protests against the city's Christian Chinese governor "Ahok".

An estimated half a million people were killed over the next few months.

The Dutch oil worker's cook would almost certainly have been murdered — as was almost every suspected communist taken into custody.

The incident is detailed in a US diplomatic cable declassified this week — part of a release of 30,000 pages that make it clear that the western embassies in Jakarta knew all about the anti-communist massacres of 1965 and 1966 — cold-blooded killings that have never been acknowledged by the Indonesian authorities.

Reports of widespread executions were coming in to the US embassy from across Indonesia: dozens of bodies floating down rivers; railway stations unmanned because workers feared for their lives; Muslim youths cutting the throats of anyone who dared criticize Islam; clerics urging the murder of communist party members "the shedding of whose blood is comparable to killing chickens"; soldiers handing over groups of 15 prisoners each night to local vigilantes to be killed.

Major General Suharto attended the funeral of five generals assassinated during the failed coup that sparked the massacre. ( AP: file photo )

There wasn't much the foreign embassies could do about the killings, even if they'd wanted to — and US officials, behind the embassy walls, were cheering things on.

It's important, of course, to remember the context of the killings: by November 1965 America was pouring troops into Vietnam and had just suffered heavy losses in its first head-on battle with the communist North Vietnamese Army.

In Indonesia, finally, the communists were on the back foot. Anti-Americanism encouraged by President Sukarno was weakening by the day as leftists were arrested and murdered.

US embassy staff were thrilled at the anti-communist fervour sweeping the nation and even discussed ways of helping in any action against the Indonesian Communist Party (PKI).

After detailing the slaughter of PKI prisoners in the provinces, one cable goes on to praise a campaign in Jakarta that "may lead to the showing of American movies in Indonesia".

What happened is barely discussed

Most Indonesians won't hear much about these newly-released diplomatic cables.

What really happened in 1965 is barely discussed here. The carnage isn't taught in schools.

Films about the killings, like Joshua Oppenheimer's extraordinary The Look of Silence, are banned here.

Intelligent discussions on the subject are shut down by mobs.

Instead, the military organises screenings of one-sided, bloodthirsty propaganda films like Pengkhianatan G30S/PKI (Betrayal of the Communists).

The groups behind the 1965 killings — the military, and Muslim organisations like Muhamadiyah and Nahdlatul Ulama — are still extremely powerful and will not tolerate any hint of a reckoning.

The Dutch official's cook will remain where he is: unnamed, his fate unknown — a sad anecdote in a yellowing diplomatic cable.