Adi Rukun and his mother in "The Look of Silence," a film by Joshua Oppenheimer (Drafthouse Films and Participant Media)

Horror movies have nothing on the terrifying reality of Joshua Oppenheimer’s documentaries.

The Act of Killing,” released in 2012, and last year’s “The Look of Silence” revisit the Indonesian genocide of 1965-1966. As many as 1 million civilians were slaughtered, and the killers were never prosecuted. Instead, they ascended to the highest posts in government and lorded their violence over a populace that’s been scared into silence.

In Oppenheimer’s movies, the perpetrators are only too happy to describe strangling, beating and butchering their victims, not to mention what it’s like to drink the blood of the dead.

But that’s only part of the story. Now that the movies are released and “The Look of Silence,” like its predecessor, is up for an Oscar for best documentary, Oppenheimer is ready to champion a cause — and it’s not the usual awards-season self-promotion.

“When something as seemingly frivolous as an Oscar nomination shines a spotlight on the film, you want to use that moment to make as big a difference as possible,” he explained during a recent trip to Washington. So he’s spreading the word that “the Indonesian genocide isn’t just Indonesian history — it’s also American history.”

You see, the U.S. government had a role in the massacre, which targeted Communists during the Cold War (although many of the murdered had no affiliation with PKI, the Indonesian Communist Party). There’s proof that the American Embassy gave Indonesia’s military lists of names of suspected Communists and was aware of the scale of the violence. But the dirtiest details of our country’s role will remain a mystery until secret government documents are declassified.

And that’s proving extremely difficult.

Director Joshua Oppenheimer: “When something as seemingly frivolous as an Oscar nomination shines a spotlight on the film, you want to use that moment to make as big a difference as possible.” (Marvin Joseph/The Washington Post)

So on a recent Tuesday morning, Oppenheimer appeared at the Dirksen Senate Office Building to meet with three Foreign Relations Committee staffers. It was the next step in getting more lawmakers to support a resolution by committee member Sen. Tom Udall (D-N.M.) to acknowledge the U.S. role in the events, unseal relevant documents and encourage Indonesia to form a truth commission.

Oppenheimer showed up a little later than expected carrying an enormous backpack. He’s almost monklike in appearance and demeanor. Bald and wide-eyed yet soft-spoken and serene, he comes across as both brilliant and a little dreamy.

But sit him in front of an audience, and Oppenheimer commands attention. He speaks in expertly honed talking points that include multiple incantations of his four-word mantra — “truth, justice and reconciliation.”

To his right, John Sifton of Human Rights Watch occasionally interjected with incredulous addenda.

“The documents are 50 years old,” Sifton said, riling himself up in support of Oppenheimer. “Let it go!”

And to Oppenheimer’s left sat Adi Rukun, the gentle, sweet-faced hero of “The Look of Silence.” The movie follows the optometrist as he visits a handful of perpetrators, ostensibly to check their eyes, but also to ask them about their roles in the murders.

A translator whispered into Rukun’s ear as he sat motionless, his head slightly cocked. His impassive expression and slightly furrowed brow were identical to the look he bore in the movie while watching Oppenheimer’s video footage — footage of men describing in grotesque detail how they tortured and murdered his brother.

But how much of a difference can a movie really make?

It turns out, quite a lot. Oppenheimer’s documentaries have already had an effect in Indonesia, where they are available free online, although the movies are officially banned.

Indonesians who had been too afraid to talk about the genocide are finally speaking up. And those who believed the government-sponsored propaganda and whitewashed textbooks — which declared the slaughter a heroic act — are seeing things differently. Rukun, meanwhile, has become something of a celebrity, and for the first time in his life, he feels liberated.

”The Look of Silence” depicts an Indonesian classroom where students are being taught that the killings of 1965-1966 were a good thing. (Drafthouse Films and Participant Media)

Before making the movie, “we were always afraid,” he said, with Oppenheimer translating. “We were always being intimidated, extorted, threatened and terrorized, and making this film and speaking out about this was a way to stop those terrifying conditions.”

According to historian Bradley Simpson, an associate professor at University of Connecticut, “The Act of Killing” was “a rather large pebble in a much longer stream of work by scholars and activists dating back to 1998.

“What it has done is provide a widely available counternarrative to the state-sponsored narrative of what happened in Indonesia in 1965 and ’66 that dominated public education and civic life for 32 years,” Simpson explained.

Simpson has spent decades investigating the 1965 genocide, including the United States’ role. Just last week, he received a response to a Freedom of Information Act request he filed 12 years ago. After being denied the release of about 1,700 documents, he did receive 17 pages of meeting notes from a National Security Council oversight committee, from the archives of Lyndon Johnson’s presidential library. But nearly all the text was redacted.

Oppenheimer is hoping to coast on the buzz of an Oscar nomination to make some headway. In addition to his stop at Dirksen, he had a couple of meetings at the State Department, including time with Tom Malinowski, assistant secretary for the bureau of democracy, human rights and labor, who tweeted his support.

It’s a process.

“You can’t just waltz in and say, ‘Hey, declassify these documents,’ ” Sifton, of Human Rights Watch, explained. But similar documents have been declassified in the past, namely those related to the United States’ role in aiding coups and authoritarian governments in Latin America.

“Can it happen?” Sifton said. “Absolutely. Is it going to be a painful, annoying, interagency battle where we need to enlist the help of the Senate Foreign Relations Committee and Senator Udall to push the administration in the right direction? Yeah, probably.”

Yes, a Senate resolution would be only advisory, because the White House has the final say. And it’s the president’s involvement that inspires Sifton. After all, President Obama has two more trips planned to Asia during the final months of his term. And what if, on one visit, he stops in Indonesia, where he lived for four years as a child, and makes a statement about accountability or, better yet, hands over those sealed documents? Sure, it sounds like a long shot, but a guy can dream.

Other documentaries have inspired action in the past. Channel 4 in England aired “Sri Lanka’s Killing Fields” in 2011, and the resulting uproar over the depictions of atrocities during the 2009 Sri Lankan civil war was huge. American congressmen and British Prime Minister David Cameron joined the conversation, calling for an investigation and demanding accountability.

The key is getting the movie in front of people. The nomination alone could raise awareness, but a win would be even better.

Like the prognosticators, Oppenheimer has a feeling the Amy Winehouse documentary “Amy” may beat him.

But there are more important things to worry about than gold statuettes. He hopes “the two films will continue to serve not just as a window to one particular terrible political situation on the other side of the globe but a mirror in which we see impunity all around us,” Oppenheimer said. “And where we recognize how we’re all touched by impunity.”