This new documentary about the Indonesian genocide is so crazy you won't believe it really happened

Following a failed coup attempt on the Indonesian government by the Indonesian Communist Party in 1965, a horrific purge of Communists from the sovereign state was conducted that included the formation of death squads that conducted mass killings of men, women, and children.

Often that included squads killing their neighbors or those they knew. Estimates put the death toll at 1 million.

At the request of victims' families, filmmaker Joshua Oppenheimer has been confronting the now elderly death-squad members since 2003. However, since the failed coup, a generation of Indonesians have been taught that the killings were warranted, and the death-squad members have been regarded as heroes.

This led to Oppenheimer making the Oscar-nominated 2012 film "The Act of Killing." To expose the atrocities committed within a nation where those in power deemed it lawful, Oppenheimer gained the trust of some of the most high-ranking members of the death squads and persuaded them to reenact their killings in the style of Hollywood genres, like a black-and-white film noir or musical number.

"It was like wandering into Germany 40 years after the Holocaust if the Nazis had won," Oppenheimer told Business Insider of the experience.

The result is powerfully effective. The film's main character, death squad leader Anwar Congo, though seemingly proud to do the reenactments, even bringing his grandchildren to watch the footage Oppenheimer shot, by the end of the film is riddled with guilt.

In the final scene, while Congo tries to describe to Oppenheimer on camera how he killed one of his victims, he begins to get sick. The film ends with Congo unable to talk and dry-heaving as he walks off camera.

Now Oppenheimer brings us the second and final film on the atrocities, "The Look Of Silence" (in theaters Friday).

This time, the filmmaker follows Adi, an Indonesian from a small village whose brother was killed by the death squads, as he confronts the members responsible for the killing.

To successfully film these "confrontations," as Oppenheimer described them to Business Insider, he said the making of "The Act of Killing" was crucial. 

"We could not shoot 'The Look of Silence' until I became kind of untouchable by the local authorities by having made 'The Act of Killing,'" Oppenheimer explained. 

In the early 2000s, Oppenheimer tried to make a film about Adi's family and other victims of the killings. But soon he realized that he and the families were in danger, as the authorities were watching them. That led to Oppenheimer's journey to film the perpetrators instead and gain their trust.

Though "The Act of Killing" had not been released in theaters yet when Oppenheimer began shooting "The Look of Silence," the ability to go to the killers in Adi's village and tell them he had just filmed a movie that featured the highest-raking members of the death squads was enough to keep him protected.

"They would not dare to physically attack me," said Oppenheimer. "It was as if you went to a small town in American and you said you were with the president of vice president, they would hesitate to beat you up or call the police."

"The Look of Silence" is even more chilling than "The Act of Killing" because of the inclusion of a victim's family. Adi and his mother and father often see the killers of his brother, Ramli, as they live in the same village. But that doesn't stop the killers from boasting to Oppenheimer what they did. Even taking him to where they killed Ramli and hundreds more.

Oppenheimer showed Adi the footage he shot of the killers and even filmed him watching it. 

Then it was time for Adi to confront the killers. To make it possible for this to happen, Oppenheimer told the killers he was bringing along Adi, who is an optometrist by trade, for his follow-up interviews with them and that in appreciation for cooperating he would test their eyes and give them as many pair of glasses they desired free of charge. But Oppenheimer also told the death squad members that Adi had a personal history with the killings.

This led to incredible exchanges between a calm and calculated Adi and the killers.

Oppenheimer called one particular meeting, between Adi and killer Inong "the most important thing I've learned doing these films" as it showed "the human capacity for evil depends entirely on our ability to lie to ourselves."

Oppenheimer tracked down Inong and learned he was one of Ramli's killers. Oppenheimer even filmed Inong describe in detail how Ramli was murdered, footage that Adi would later watch.

While getting his eyes tested by Adi, Inong begins to brag about the killings.

"It was almost like the stories were dangling in the air to both impress and frighten Adi," said Oppenheimer. "He said 'Everyone in my community is afraid of me,' and you understand through these stories he's telling that he wants to keep people afraid. He's talking with these test lenses on and he kind of looks like a demon.

"When I saw this I moved the camera right on Inong's face. Twitching as he waited for the response to his awful, unthinkable stories."

However, Inong was caught off guard by Adi's counter, as he questions the killer's actions and what right he had to kill innocent people.

In this exclusive clip given to Business Insider, you can see how tense the encounter got:

"All the perpetrators are human and they therefore know the difference between right and wrong," said Oppenheimer. "So they need an excuse, and cling to it forever after they commit the crime. I think that's why Inong gets so angry at Adi. He's trying to protect the lie because without it he's not sure how he'll live with himself."

Oppenheimer said when he wrapped filming this scene Inong was upset with him.

"He said to me, 'How dare you bring a communist to my house!'" Oppenheimer said. "For tactical reasons I tried to calm things down as best I could so Adi and I didn't leave and suddenly are pursued by the police."

Watch the trailer for "The Look of Silence."