The study, which focused not only on mass shootings but other acts of targeted violence such as knifings, bolstered previous research on the warning signs students often exhibit before committing deadly violence at their school.
The Secret Service, which is primarily tasked with protecting the U.S. president and other elected officials, has analyzed school violence since the 1999 mass
shooting at Columbine High School in Colorado.
The report did not include the deadliest shooting at a high school in U.S. history, the killing of 17 people at Stoneman Douglas High School in
Parkland,
Florida, that a lone gunman carried out on Feb. 14, 2018.