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ST. PAUL, Minn. (AP) -- Two St. Paul researchers who tracked patterns among school shooters say Minnesota's policies that focus on lockdown drills and security infrastructure get school safety wrong.

Hamline University criminology professor Jillian Peterson and Metropolitan State University criminal justice professor James Densley have been collecting data about individuals who committed gun violence in U.S. schools.

Peterson and Densley found patterns, such as current or former students having a history of trauma or expressing suicidal thoughts.

The researchers say their data shows that Minnesota's strategy of investing in more secure buildings is inadequate in preventing school shootings. The professors say the research points toward the need for more mental health support in schools.

Peterson says schools need to approach threats of violence as a point of intervention.