On Oct. 26, 2015, Indonesian President Joko Widodo met with President Obama, saying his country intends to join the Trans-Pacific Partnership trade deal. (Reuters)

Fifty years ago today, the U.S. Embassy in Indonesia sent a cable to the State Department asking for funding to help civilian groups that the United States knew were engaged in a violent effort to eliminate communist influence in Indonesia. At the time, these civilian groups and the Indonesian military, led by Gen. Suharto, were massacring and purging communists and suspected communists, in response to what the military alleged was an attempted coup on Sept. 30, 1965.

The ensuing civilian-military campaign resulted in the mass killing of about 500,000 people. Around 750,000 more civilians were imprisoned, tortured and discriminated against for decades. This marked the beginning of a shift to military rule in Indonesia. The highly repressive military has retained influence. Reforms have been slow and incomplete, even after Indonesia’s transition to democracy in 1998-99. Those responsible for the mass violence have never been punished.

The documentaries “The Act of Killing” and “The Look of Silence” have brought greater attention to the massacres and the impunity their perpetrators enjoy. But Indonesian forces are not solely responsible for what happened.

[Joshua Oppenheimer talks about ‘The Act of Killing’]

As I explore in a forthcoming book chapter based on declassified government documents, U.S. officials were accessories to this mass murder. The United States helped create the conditions for the killings. It supported, rather than restraining or condemning, the perpetrators. The United States was not alone; British and Australian officials also supported the killings.

The United States has never officially apologized, though, for its involvement in what the CIA called “one of the worst mass murders of the 20th century.” America also continues to support the Indonesian military despite its culture of repression. In fact, during Indonesian President Joko Widodo’s visit to the United States in late October, President Obama and he largely ignored human rights issues.

In the early 1960s, Indonesia had a left-wing president, Sukarno, and the third-largest communist party in the world, the PKI. The U.S. government believed that Sukarno and the PKI were threatening to make Indonesia the “next China,” endangering U.S. strategic and commercial interests. The United States took covert action against Sukarno in the 1950s and restricted aid in the 1960s, primarily funding military assistance programs. U.S. officials cultivated relationships with anti-Sukarno leaders. In February 1965, as tensions were rising in Indonesia, the United States approved a covert action plan to “chip away at the PKI” through “black letter operations” and support for anti-communist groups.

The political situation exploded Sept. 30, 1965, when a group of junior military officers killed six top generals. By the next day, the army, under the command of Suharto, had crushed the officers. There is no evidence that the Sept. 30 attack was organized by the PKI or part of a larger plot, yet Suharto moved quickly to smear the PKI and leftist organizations and painted the events as a communist coup attempt. The military sidelined Sukarno and immediately launched a campaign with student and Muslim organizations to “crush” the PKI.

U.S. officials had long hoped that the military would repress the PKI and moved to bolster the military. On Oct. 5, Ambassador Marshall Green recommended that the United States spread anti-PKI propaganda, and Secretary of State Dean Rusk wanted to encourage the military “to follow through against PKI.” By Oct. 12, aware that the army was organizing anti-communist attacks, the United States secured assurances that the British would stand down from their confrontation with Indonesia in Malaysia to allow the Indonesian military to “straighten things out” domestically.

Later that month, Green expressed approval that the military was “working hard at destroying PKI” through executions, and Rusk affirmed U.S. support for the “elimination of the PKI.” U.S. officials also provided detailed lists of thousands of PKI members for the military and anti-communist civilians, with American officials reportedly checking off who had been killed or arrested.

Amid reports of massacres throughout the country, in late October, Rusk and U.S. national security officials made plans to unconditionally provide weapons and communications equipment to the Indonesian military, while new U.S. aid was organized in December for the civilian anti-communist coalition and the military. By February 1966, Green stated approvingly that “the Communists…have been decimated by wholesale massacre.” U.S. support deepened in March 1966 as the military pushed Sukarno further off the scene, with the United States releasing economic aid that was frozen while Sukarno was in power, even as killings slowed but continued through 1968. In September 2015, the CIA released Presidential Daily Briefings from Lyndon Johnson’s administration confirming that Johnson was well aware of events in Indonesia and did nothing to halt the killings.

Suharto remained in power until 1998, retaining strong U.S. support. U.S.-Indonesian military ties likewise continued, despite Indonesia’s illegal, deadly 1974-1999 occupation of East Timor and its ongoing highly repressive counterinsurgency campaign in West Papua. Research has shown that governments that commit one mass killing and remain in power, like those of Suharto, Slobodan Milosevic and Saddam Hussein, are likely to employ these tactics again. Close allies are best positioned to pressure governments to avoid or halt mass atrocities. But in the Indonesian case, the United States assisted and encouraged the killing.

In a January 1966 speech, Sen. Robert Kennedy said, “We have spoken out against inhuman slaughters perpetrated by the Nazis and the Communists. But will we speak out also against the inhuman slaughter in Indonesia, where over 100,000 alleged Communists have been not perpetrators but victims?” Kennedy argued that the United States must speak out against all mass killings. If the United States explicitly acknowledged and atoned for its role in the violence that engulfed Indonesia in the 1960s, it could help Indonesia confront its past and move toward justice and reconciliation.

The survivors and relatives of victims still suffer from discrimination in Indonesia, and the alleged threat of communism is still used to justify political and social repression.

Half a century after the massacres began, Widodo and his ministers have refused to apologize, espousing the false narrative that the PKI bear equal responsibility for the violence, even though there was minimal PKI resistance at the time. Perpetrators still hold positions of power locally and nationally.

[Will Indonesia’s presidential election be stolen?]

If the United States were to pressure the Indonesian government and military to follow international law, it could help minimize or even prevent contemporary abuses in West Papua and elsewhere in the country. Sen. Tom Udall (D-N.M.) has twice proposed a ‘Sense of the Senate’ resolution seeking both a truth and reconciliation commission in Indonesia and further clarity on the U.S. role in the massacres, though this has not spurred further legislative or executive action. U.S. acceptance of responsibility for its own role in the massacres could reinforce American human rights rhetoric and bolster the claims of survivors and victims’ families in Indonesia.

Kai Thaler is a PhD candidate in the department of government at Harvard University, studying civil wars, political violence, and state building, and is on Twitter @KaiMThaler.