Osage killings: The mystery mass murder of some of America's richest people

It’s a mass murder story largely forgotten in the world's history and one that took place less than 100 years ago.

In his latest nonfiction book, “Killers of the Flower Moon,” New Yorker writer and bestselling author David Grann investigates the mysterious murders of members of the Osage Indian tribe of Oklahoma in the 1920s.

The Osage was a small tribe whose members became some of the richest people in America. Through treaties with the government in the early 1900s, the tribe had retained oil and mineral rights to the land members had been forced to live on in Osage County, Okla.

By the 1920s, the oil deposits beneath the land made them rich, but they also became targets. Members of the tribe began dying under mysterious circumstances, one after another.

Grann sat down with Yahoo Global News Anchor Katie Couric to talk about his new book, the mystery behind the murders and the A-listers rumored to be attached to the movie adaptation.

“Mollie Burkhart is this remarkable Osage woman. She was born in a lodge in 1886, speaking only Osage. Because of the oil money, within a few decades, she’s living in a mansion. She’s married to a white settler from Texas,” Grann explained.

“And in 1921, she becomes a prime target of this conspiracy.”

Burkhart’s sister, Anna, is found shot dead in a ravine near their home. Her mother becomes mysteriously sick and also dies. Her younger sister, Rita, is killed, along with her husband and servant, when her house is blown up in the middle of the night.

"That’s just Mollie’s family. Other Osage were being systematically targeted,” Grann said.

“By 1923, officially the death toll had surpassed more than 24 Osage. And many of those who tried to catch the killers were also killed.”

The killers were conspiring to gain access to the headrights of the Osage people which, as Grann explained, would in turn give them access to the oil money.

“The only way you could get a headright to get this money that was coming in regularly from the oil money was through inheritance. And so the conspirators, what they would do is they would direct people to marry into the family,” he said.

“Then one by one, slowly eliminate them so that they were inheriting more and more of these headrights, more and more of these millions.”

The murders were making headlines across the country. No one could figure out who was murdering these members of the tribe until a young J. Edgar Hoover and the FBI took over the case. Hoover hired a Texas cowboy, Tom White, who traveled to Oklahoma and cracked the case to bring the killers of Mollie Burkhart’s family to justice.

“This conspiracy really was about not who did it, but who didn’t do it. And that there really was a culture of killing,” Grann said.

When Couric asked why these murders happened, Grann replied with a simple answer. “Money. Money and prejudice.”