In the town of Fairfax, Oklahoma, the fact that life was good for the Osage Indians in the late 1800s might have seemed to some like sweet justice. 

For the reservation they had been shunted to decades earlier had turned out to be brimming with oil, and the tribe put it good use by building mansions, buying cars and sending their children to private schools.

But, by the time the 1920s came around, at least two dozen of them had been murdered by being shot, poisoned and blown up - and no one knew who was responsible. 

This is the true story behind director Martin Scorsese's latest partnership with Hollywood superstar Leonardo DiCaprio, in upcoming film Killers of the Flower Moon.

In what was the first major murder case of the Federal Bureau of Investigations (FBI), agents ended up tracing the killings to a disgruntled group led by 'cattle king' William Hale, who was jailed for more than two decades for his part in the murders.

He had encouraged his nephew to marry into the Osage tribe as part of a plot to win their oil rights.