Sadly, just two months later, Anna’s mother, Lizzie Q, “suspiciously died,” and two years later, her cousin Henry Roan was shot to death. To make it all even wilder, in March 1923, Anna’s sister and brother-in-law, Rita and Bill Smith, were also killed when their home was bombed. Anna’s last sibling, Mollie Burkhart, was devastated and suspiciously came down with an ongoing illness. At least two dozen Osage Native Americans, a prominent oilman, and others had turned up dead. The FBI claims that many private detectives and other investigators turned up nothing, so the Osage tribe turned to the federal government, and Bureau agents were briefed on the case. 

Source: https://www.buzzfeed.com/consheabrown1/solved-and-unsolved-cases-from-the-fbi