From 2006 to 2017, there have been more than 350 mass killings in the United States.

Well-known images from Newtown, Aurora and Virginia Tech capture the nation's attention, but similar bloody scenes happen with alarming frequency and much less scrutiny.

USA TODAY examined FBI data -- which defines a mass killing as four or more victims -- as well as local police records and media reports to understand mass killings in America. They happen far more often than the government reports, and the circumstances of those killings -- the people who commit them, the weapons they use and the forces that motivate them -- are far more predictable than many might think.

Yet no one is keeping track.