Hamline News

Comprehensive Database of Mass Shooters Released for Public Use


The Violence Project, a nonpartisan think tank, have publicly released the largest, most comprehensive database of mass shooters in the United States.

This new database, funded by the National Institute of Justice, the research arm of the U.S. Department of Justice, was developed by professors Jillian Peterson and James Densley and a team of students at Hamline University in St. Paul, Minnesota. It includes 171 mass shooters from 1966 to 2019, each coded on 100 pieces of life history information. The entire database is downloadable for free at The Violence Project website.

“Mass shootings are a complex issue, requiring multiple avenues of prevention,” says Dr. Jillian Peterson, “The goal of this project is to ground our public policy discussions in data and develop evidence-based policies to prevent these tragedies.”

The mass shooters in the database each shot and killed four or more people in a public space, including schools and houses of worship. They are ninety-eight percent male and fifty-two percent white, with an average age of thirty-four.

Most mass shooters were in crisis prior to the shooting and suicidal, and almost half of them leaked their plans in advance. Sixty-two percent of mass shooters had a criminal record and fifty-seven percent had a violent history. Seventy percent of mass shooters knew at least some of their victims.

This database is the first to look closely at the mental health histories of mass shooters. Among the 171 mass shooters, two-thirds had a mental health diagnosis or presented mental health concerns. This is only slightly higher than the fifty percent of people in the general population who will meet criteria for a mental illness in their lifetime. However, a mental health diagnosis does not mean that the actions of mass shooters are directly motivated by their symptoms.

The database shows that sixteen percent of mass shootings are at least partly motivated by psychosis – which is less than the percentage that of shootings motivated by domestic issues, employment changes, interpersonal issues, and hate.

This is also the first database to look closely at how many shooters obtained their guns. The majority of mass shooters use handguns (seventy-seven percent) and twenty-five percent used assault rifles. Of the known data, seventy-seven percent of shooters purchased at least some of their guns legally, thirteen percent made illegal purchases, and nineteen percent stole guns.

“Mass shootings have increased in recent years, both in the number of incidents and the
number of people killed”, Dr. James Densley explained. “Mass shootings are rare but routine events. We now have the data to understand that routine and disrupt it before it’s too late.”