If you have already seen Martin Scorsese’s latest film, “Killers of the Flower Moon,” you know about the “Reign of Terror” that ravaged the Osage Nation in Oklahoma in the 1920s. In fact, the movie is based on a shocking true story that changed the Osage community forever.

The new film is based on David Grann’s 2017 book “Killers of the Flower Moon: The Osage Murders.” The nonfiction tale details how people like white war veteran Ernest Burkhart and his uncle William K. Hale murdered Osage members in cold blood. It also extensively depicts the FBI’s eventual investigation.

However, Scorsese chose to slightly depart from that perspective in the film, bringing it closer to the Osage community’s viewpoint.

“After a certain point, I realized I was making a movie about all the white guys,” the director told TIME. Scorsese eventually had a “touchstone” meeting with Osage members in 2019 and changed the script. The movie now centers on the real-life story of Burkhart and his Osage wife, Mollie Burkhart, whom he slowly poisons in the film.

“I was not going to make a picture in which a few Osage would just be victims in the background,” Scorsese told The Guardian. “We were approaching the project in a very different spirit.”

After hiring many Osage members to take part in the movie, the director created a film intent on capturing the “very nature of the virus” that led to the “genocide” of the tribe. Here is what you should know about the true story of the “Reign of Terror,” and how it may have had more accomplices and deaths than the film portrays.

After the discovery of vast oil deposits, Osage members became extremely wealthy

The movie “Killers of the Flower Moon” depicts the true story of the Osage Nation in the early 20th century. It zeroes in on the decades following the tribe’s move to Osage County, Oklahoma, their eventual extreme wealth, and the tragic murders that became a part of their history.

Author Grann wrote for PBS that the Osage were driven off their original land in Kansas in the 1870s. They settled on a “presumably worthless” area in Oklahoma — which made them some of the richest people in the world.

That Oklahoma reservation was actually home to one of the largest oil deposits in the country. This is especially significant because the Osage Nation had already negotiated a headright agreement with the United States government. As per TIME, every “full-blood Osage” received 657 acres of land, and a headright passed down generations.

Once the oil was discovered in 1894, the Osage became very rich. According to New York Times, the community sat atop the equivalent of today’s $540 million, and many members had chauffeurs and mansions.

Grann explained to USA Today just how wealthy the Osage Nation became. “Because of the vast oil deposits on their lands, by the 1920s, the Osage were among the wealthiest people per capita in the world.”

However, a federal ruling later prohibited them from controlling their own money. In fact, the government gave them Caucasian guardians who administered their finances and sometimes stole from them. Chief of the Osage Nation, Geoffrey Standing Bear, described to The Guardian: “It’s not, who was complicit? It’s who wasn’t complicit?”

Even more, only 6,000 out of 21,000 Osage members have oil rights today. “We estimate 1.5 [billion] barrels have been removed from our lands in all this time,” Chief Standing Bear revealed to the outlet.

Still, in the 1920s, the Osage’s wealth set the scene for the eventual “Reign of Terror” — which claimed up to “hundreds” of members’ lives.

The author of “Killers of the Flower Moon” says the Osage murders involved many more accomplices

As per Grann’s research, several Osage members began dying mysteriously in the early 20th century. The family members of Mollie Burkhart, portrayed by Lily Gladstone in the movie, were “prime targets.” This included the murders of her sister, Anna Brown, who died of a gunshot to the head, and Burkhart’s mother, Lizzie Q. Kyle, who is believed to have been poisoned.

Several of Mollie Burkhart’s family members were killed during this time, including her sister Minnie. Burkhart’s sister Rita Smith, her husband Bill Smith, and their maid Nellie also died after someone bombed their home in 1923.

Harrowingly, Mollie Burkhart’s own husband, Ernest Burkhart, and his uncle, William K. Hale, were later convicted for some of her family member’s murders.

As depicted in the film, real-life Ernest Burkhart and his uncle conspired the marriage to Mollie — and the murders of Osage members — to take their headrights.

This “Reign of Terror,” which mostly spanned from 1921 to 1926, claimed the lives of at least 24 Osage members in an attempt to steal their wealth. However, while the movie largely focuses on Ernest Burkhart and his uncle Hale’s crimes, Grann says there were many more conspirators and murders.

“The real murders were less about a singular plot or evil figure with henchmen, but rather many killings that were never properly investigated,” Grann explained.

The author also noted how accomplices included many more people than those who wielded weapons. “Many people were complicit: doctors with their poison, morticians covering up causes of death, lawmen staying silent.” Even more harrowing, there may have actually been “hundreds” of murders.

As former Osage Nation Principal Chief Jim Gray wrote, the true story of the “Reign of Terror” still cuts deep. “My great grandfather, Henry Roan was one of those murdered during this era,” he described. “[The FBI] uncovered the larger scheme underway to wipe out an entire Osage family and their headrights, which were worth millions.”

Adding, “That’s the story I was told by my family and I always held back the raw emotions that his death brought to our family.” Mentioning that both his mother and father, who were born in the 1920s, were “orphans by the end of the decade,” he said this history is still “vivid,” to him.

“Our wealth put a target on our back,” he added.

According to TIME, the deadly explosion in Rita and Bill Smith’s home led to the FBI’s involvement. Agents found evidence that Hale, Ernest Burkhart, Burkhart’s brother Bryan, and several others had conspired in the Osage members’ murders.

By 1926, authorities arrested Hale and Ernest Burkhart. While Burkhart confessed after his arrest for the murders of Rita Smith, Bill Smith, and Nellie White, it seems like Hale never admitted guilt. Grann told USA Today: “There was something unquestionably evil about Hale, at his core.”

Later, a court sentenced Burkhart, Hale, and convicted murderers John Ramsey and Kelsie Morrison to life in prison. However, Burkhart received a pardon in 1966.

Meanwhile, Mollie and Ernest Burkhart divorced, and she later remarried.

“Killers of the Flower Moon” addresses the systemic way Caucasians attempted to take away wealth from Osage members, and killed them in the process.

As Scorsese described to BFI, “Well, we are complicit… We simply are.”

“We’re all the killers. The European white comes in, Western civilization comes in,” the director added. “We are the killers, and we have to understand that. We have to confront it in ourselves.”