In 1990 some US officials admitted that they provided lists of thousands of suspected communists to the army:

“It really was a big help to the army,” said Robert J. Martens, a former member of the U.S. Embassy’s political section who is now a consultant to the State Department. “They probably killed a lot of people, and I probably have a lot of blood on my hands, but that’s not all bad. There’s a time when you have to strike hard at a decisive moment.”

In 2017 some documents were declassified which shed more light on the US’s complicity:

The U.S. government had detailed knowledge that the Indonesian Army was conducting a campaign of mass murder against the country’s Communist Party (PKI) starting in 1965, according to newly declassified documents posted today by the National Security Archive at The George Washington University. The new materials further show that diplomats in the Jakarta Embassy kept a record of which PKI leaders were being executed, and that U.S. officials actively supported Indonesian Army efforts to destroy the country’s left-leaning labor movement.

The 2012 documentary The Act of Killing 🧲 is probably the most disturbing film I’ve ever seen. In his acceptance speech for the Best Documentary BAFTA award, the director said this:

I urge us all to examine ourselves, and acknowledge that we are all closer to perpetrators than we like to believe. The United Kingdom and United States helped to engineer the genocide, and for decades enthusiastically supported the military dictatorship that came to power through the genocide. We will not have an ethical or constructive relationship with Indonesia (or so many other countries across the global south) going forward, until we acknowledge the crimes of the past, and our collective role in supporting, participating in, and, ultimately, ignoring those crimes.

… but the British Academy of Film and Television Arts edited that part out of the video they posted online.