The journalist and author David Grann indulges his readers to the investigating of the wealthy Osage people that took place in Osage County, Oklahoma back in the 1920s immediately after large oil deposits were found on the land they owned. Officially the count of the murdered is at least 20, but Grann suspects and puts forward evidence that suggest that the real number may reach into the hundreds because of the ties to the oil (Wikipedia entry).
Tied in with the complicated relationship of the native peoples of the time and the allotment system of laws that were being imposed on them, there’s nothing simple about these strings of killings. A sad tale of greed and serious racial hatred that saw poor white farmers so enraged that natives would have more money than they did that they were willing to kill the women of the Osage tribe one by one until they died out and had to bequeath the money to white men. This book is the story of some serious historical injustice and the formation of the FBI whose first investigation was the killing of the Osage.