A study conducted by the Secret Service found that school shootings are preventable when possible shooters showed warning signs before their attacks. 

The study released Tuesday found that 67 planned school attacks over the course of 12 years were stopped because the perpetrators gave off warning signs to family and friends, even telling them what they were about to do. 

The report was authored by Lina Alathari, a psychologist who leads the agency's National Threat Assessment Center, according to a report by NBC News.

Alathari found that many planned attacks could be thwarted when people took notice of warning signals. Such signals include students having an interest in guns, suicidal thoughts, a fascination with past violent attacks and harassment of others. In the study, half of the people who had been plotting shootings had been bullied by their peers as well. 

The Secret Service also shared that students can plan their attacks for months; 21 of the 67 planned attacks were plotted in that range of time. One was plotted for over two years. 

Alathari said that school violence is preventable when communities can see a person showing warning signs.  

“That should involve teachers, counselors, administrators, principals and school resource officers. Everyone has a role to play in the prevention,” Alathari said.