Spoiler alert! This story includes detailed plot points of the new movie "Killers of the Flower Moon" and the real-life events on which it's based.

The new Martin Scorsese movie “Killers of the Flower Moon” plays like an improbable human horror story, brimming with deceit and death in 1920s Oklahoma.

The 3-hour-and 26-minute film, starring Robert De Niro, Leonardo DiCaprio and Lily Gladstone, tells the story of Osage Nation tribal members, newly wealthy from the discovery of oil on their otherwise parched reservation lands, and the duplicitous non-Native Americans who swoop in to steal their bounty.

But while it plays like an allegory, the story is true. Based on the best-selling 2017 book by journalist David Grann, “Killers” is the result of years of research and interviews with Osage elders. The tale explored both the deaths surrounding the family of Mollie Burkhart (Gladstone) as well as the exploits of the nascent Federal Bureau of Investigation.

USA TODAY spoke with Grann to get details on how the movie compares with his book.

Were the Osage Indians as rich as the movie ‘Killers of the Flower Moon’ shows?

“Absolutely,” says Grann. “Because of the vast oil deposits on their lands, by the 1920s the Osage were among the wealthiest people per capita in the world.”

People of the Osage Nation had been moved around by the federal government for years before winding up in a barren stretch of Oklahoma, which wasn’t worth much at the turn of the 20^th century. But when oil deposits were discovered, everything changed.

Grann says that in 1923, with roughly 2,000 people on the tribal rolls, the group “collectively got more than $30 million (in payments from oil companies leasing their land),” which translates to about $500 million in today's dollars. And while “few Americans owned a car at that time, many Osage had numerous cars, as well as many servants, often white.”

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How many Osage Indians were murdered in order to steal their oil rights?

Grann says at least 24 Osage tribal members were murdered in order to get their oil rights, so-called “headrights.” A typical way to get these rights was marrying into an Osage family. But as the book and movie explain, sometimes there were shootings or slow poisonings to make the deaths look like mysterious ailments.

While the “Killers” movie focuses on the evil schemes of one man, William Hale (DeNiro), and his hapless nephew Ernest Burkhart (DiCaprio), “the real murders were less about a singular plot or evil figure with henchmen, but rather many killings that were never properly investigated. Many people were complicit: Doctors with their poison, morticians covering up causes of death, lawmen staying silent. Many conclude the real death toll was in the scores, if not hundreds.”

Did Mollie Burkhart really meet with President Calvin Coolidge to discuss the Osage murders?

Not likely, says Grann. “There is no evidence that I know of that Mollie spoke to the president about the murders,” he says. “But it needs to be underscored that the Osage did go to Washington, D.C., and she might have been on a trip.”

Grann says Burkhart, as the movie shows, was so distraught by the deaths of her sisters that she “vigorously campaigned for justice, offering testimony when needed and hiring private detectives to help find the killers.”

Were the Osage Indian murders the first big case for the new FBI?

In 1921, a young J. Edgar Hoover, who would wind up as the notorious and longstanding director of the FBI, took over a new office then simply called the Bureau of Investigation. Hoover was eager to put his new group on the political map, so he eagerly dispatched a former Texas Ranger, Tom White (Jesse Plemons) to Oklahoma to investigate the mysterious Osage murders after local law enforcement hadn't solved the case.

“This was among the first big complex homicide investigations by the fledgling Bureau of Investigation, which would become the FBI,” says Grann. “At the time, this office had limited jurisdiction over crimes nationally, but it did have jurisdiction over crimes on federal (Native American) lands.”

Grann adds that thanks in part to this case, laws were passed in the 1930s that gave the FBI greater reach.

William Hale was convicted of links to Osage murders, but did he ever admit guilt?

“There was something unquestionably evil about Hale, at his core,” says Grann. “According to the records he did show no remorse. He had created and was reflective of a pathological ideology of western expansionism, a boosterism and a conviction' that the Native American way of life was ending. world was going.”

Hale served his time and died at 87 in Arizona in 1962.

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Was there really a Lucky Strike radio play that retold the story of the Osage murders?

At the end of Scorsese’s “Killers,” the director makes a cameo appearance as an actor in a Lucky Strike cigarette-sponsored radio play about the Osage murders, years after the case was closed..

Grann says the story was the subject of a radio play, but its purpose was less about sharing outrage of the treatment of Native Americans as glorifying the FBI's work.

“Hoover wanted it to burnish his and the Bureau’s reputation, so he organized these propagandistic retellings of what happened,” says Grann. “The scene in the movie is getting at the issue of how history is recorded, and often misrecorded. Sure, Hoover closed the case, but there was a deep conspiracy surrounding the murders that the Bureau never exposed.”