How Scorsese, DiCaprio and De Niro Made ‘Killers of the Flower Moon’

Films can take years to make, and at age 80, the director Martin Scorsese is aware he has a finite amount of both films and years left.

“He’s got many things in his head he wants to do, and I don’t know that we’ll live long enough to do them,” his longtime editor, Thelma Schoonmaker, 83, said at the Cannes Film Festival on Sunday.

Because of that, anything Scorsese commits to has to be doubly worth it, the man behind classic films like “Taxi Driver,” “Goodfellas” and “The Departed” said.

“I’m at an age now where everything I try, I want it to matter for me,” Scorsese said. “It always did, but even more so now because we’re just running out of time.”

His latest film, “Killers of the Flower Moon,” took around seven years to come together, Scorsese and his collaborators explained on a sunny Cannes terrace the day after the Apple-financed project premiered there to glowing reviews. (It will be released in theaters this October, then debut on the streaming service at a later date.)

Still, the finished film is very different than the one Scorsese and his star, Leonardo DiCaprio, originally intended to make: The material couldn’t be cracked until they were willing to throw out every notion of what they first thought “Killers of the Flower Moon” should be.

The initial version was meant to be a gripping mystery like its source material, the nonfiction book by David Grann that follows the straight-arrow F.B.I. agent Tom White as he investigates a string of murders of Native Americans in 1920s Oklahoma. There, the Osage Nation is the country’s most prosperous tribe; indeed, the discovery of oil on their land has turned them into the wealthiest people per capita in all of America. But members of the Osage are regularly dying in suspicious ways, and even though the tribe has received pledges of help from the prosperous cattle baron William Hale (played in the film by Robert De Niro), no one has yet been brought to justice.

White eventually uncovers a vast conspiracy that implicates not only the wealthy cattleman but also his nephew Ernest, who has married an Osage woman, Mollie, and stands to benefit if other members of her family perish, since their land rights will eventually make their way to his wife (and then him). This real-life twist is the revelation the book is building to, but when the screenplay by Scorsese and Eric Roth was structured in the same way, it never came alive.

“I think Marty and I just looked at each other and we felt there was no soul to it,” DiCaprio said. “It was about an investigation, and I said to Marty, once you see De Niro as Hale, you’re going to go, ‘I think I know who did it.’ What are we going to unravel?”

Instead of concealing those plot points, then, Scorsese and DiCaprio decided to lean in: Over the film’s sprawling three and a half hours, they’d let us in on the murders as soon as Hale and Ernest begin plotting them. And as the story gravitated toward those malevolent men, DiCaprio decided he would rather play Ernest instead of the lawman Tom White, a role Jesse Plemons (“The Power of the Dog”) stepped in to fill.

“The tricky thing was to work against this cliché of white savior,” Plemons said. After all, it’s white people who perpetrated these crimes, too. But the subjects of his character’s investigation have motivations that often appeared baffling, like DiCaprio’s Ernest, so loving and attentive to his wife.

“It was one of the most twisted love stories I’d ever come across,” DiCaprio said. “I can’t even believe it myself that these two people were in love and stayed together.”

De Niro still found himself at a loss for words when asked to unpack Hale, who goes out of his way to endear himself to the Osage Nation even while reducing its numbers. Did playing the role help him reconcile the man’s tendencies?

“In some ways, no,” said De Niro. “He’s a sociopath. You don’t know why he would love them and betray them in such a way.” It wasn’t simply about money, De Niro said: Hale had plenty of it already. “Greed is a real condition, but it seems like a simpler word than what has happened,” he said. “Greed can make greedy people, but they don’t behave like that.”

So what was that additional motivation that led Hale and Ernest down such dark paths? When asked, Scorsese didn’t mince words: It has to do with white supremacy, he said.

“It’s about somebody not being from European culture, or white culture,” the filmmaker said. “Just ‘not up to par,’ and therefore, it’s maybe easier to kill them. I mean, whoa! And I believe that’s real thinking.”

And it has plenty of contemporary parallels, too, Scorsese and De Niro said. At the film’s news conference yesterday, De Niro spoke about the film’s depiction of “the banality of evil” and said, “We see it today and you know who I’m talking about but I’m not going to say his name — that guy is stupid.” Later, he couldn’t help himself: “I mean, look at Trump!”

With Scorsese, I mentioned how Ernest’s willingness to carry out his uncle’s cruel orders reminded me of another film at Cannes, “The Zone of Interest,” which follows a Nazi commandant and his family, who live next to Auschwitz and ruthlessly compartmentalize the atrocities carried out on the other side of their garden wall.

“What scares me is how easy it is for all people — well, I hope not all people, but most people — to fall into that,” Scorsese said. “I’ve had a number of people say, ‘No, I think everyone is capable of that.’ I hope not. I wonder how I would act.”

To broaden the film’s perspective past these white men’s malevolent deeds, Scorsese consulted extensively with the Osage to ground the film in their traditions and lived experiences. Already, “Killers of the Flower Moon” has provided an awards-worthy breakthrough for the Native American actress Lily Gladstone, who plays Mollie, Ernest’s wife. She more than holds her own against DiCaprio and De Niro with her sly smiles and formidable center of gravity, and after the film’s premiere, cameras in the theater captured tears filling her eyes in a moment that went viral online.

On the terrace at Cannes yesterday, I asked her about it. “You mean the moment where you can visibly see me tear up and break down and try to shoo it all away,” she said, “and I turn around and Cate Blanchett and I are locking eyes — my favorite actress since I was 15?”

Gladstone said she felt a lot of things in that moment, but what she could sense most of all was that the applause, in large part, was for Mollie, a character who grew in importance as Scorsese kept revising and shaping his film.

“I was grateful that the audience saw Mollie the way they were supposed to, and the way they should have,” she said. “It was an affirmation of what fine storytelling this is. What people thought would be an impossible feat is the story we were able to do.”