We Have Studied Every Mass Shooting Since 1966. Here's What We've Learned About the Shooters

For two years, we’ve been studying the life histories of mass shooters in the United States for a project funded by the National Institute of Justice, the research arm of the U.S. Department of Justice. We’ve built a database dating back to 1966 of every mass shooter who shot and killed four or more people in a public place, and every shooting incident at schools, workplaces, and places of worship since 1999.