Commentary: We have studied every mass shooting since 1966. Here's what we've learned about the shooters
In the last week, more than 30 people have died in three separate mass shootings in Gilroy, El Paso and Dayton, Ohio. We believe that analyzing and understanding data about who commits such massacres can help prevent more lives being lost.
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
