As the world prepares for one of the biggest blockbusters of the year, Killers of the Flower Moon, the inspiration behind the movie comes from a bestselling book by author David Grann. 

Long before Hollywood movie cameras and A-list actors descended on Osage County, a New York-based journalist and author made his way to northern Oklahoma to tell a story almost forgotten with time. 

"So many Americans, and I include myself among them, knew nothing about this history,” Grann said.  

Grann is the author of five best-sellers and even more featured articles and essays. News On 6 has spoken with him several times since the book was first published in 2017. 

But his research into the Reign of Terror spans several years before that, as he told LeAnne Taylor five years ago. 

"I visited the Osage Nation museum, and they had this great panoramic photograph on the wall there, and it was taken in 1924,” Grann said. “It shows members of the Osage Nation, along with white settlers, looks very innocent. But a portion of the photograph is missing, and I asked the museum director Kathryn Red Corn, who would later become a friend, why was that missing? She had pointed to that missing panel, and she said because it contained a figure so frightening, she decided to remove it. Then she pointed to it, and she said the devil was standing right there." 

After this meeting, Grann made several more visits to Pawhuska, meeting with the Osage and descendants of those who were murdered. 

Descendants like Billy Ponca, whom News On 6 spoke with in 2019. 

"Bryan Burkhart married my great aunt. He was involved with the Anna Brown killing,” Ponca said.  

Danette Daniels is the granddaughter of a couple who had one of the last arranged marriages in Fairfax. 

"Everybody knew. But it was just so heart-wrenching we didn't really discuss it openly,” Daniels said.  

Grann would use these stories to help tell his story, one he was initially going to write in an article for The New Yorker. 

He quickly realized, though, the story was too big and decided to write a book. 

He chose the title “Killers of the Flower Moon” as a symbolic representation of tiny flowers that die in the Osage Hills every May from larger light-stealing flowers. 

The Osage refers to May as the time of the flower-killing moon. 

“Part of this journey was trying to kind of chase history and try to, hopefully, capture it,” Grann said.  

The book quickly became a success, with Time Magazine calling it one of the top ten best nonfiction books of 2017. Amazon called it the best book of that year. In the years that followed, the story caught the attention of Hollywood. 

A bidding war ensued, and the rights to the movie sold for $5 million. 

Martin Scorsese, like Grann, worked with the Osage to tell the story completely and take the message from print to the big screen. 

A few months ago, Grann told 60 Minutes he helped actors in the movie learn about the real-life characters they play. 

"Occasionally, some people will reach out to you...It's just a different world, you know. It's just a different world,” Grann said. 

The book has now sold nearly two million copies, a number that could increase as the movie is seen worldwide. 

Grann's latest book, called “The Wager,” tells the true story of a British naval ship that crashed in South America in the 1700s. It has also been auctioned off for a Hollywood movie. 

Grann hopes it and Killers of the Flower Moon reach as many people as possible.  

"One of the things that you hope with a story like this is that it will become part of our consciousness, that it will become part of our national narrative,” Grann said.  

“Killers of the Flower Moon” spent 49 weeks on The New York Times nonfiction bestseller list.