The largest single school shooting in U.S. history, which occurred at Virginia Tech in 2007, was perpetrated by Seung-Hui Cho.

CNN: Rejection, bullying are risk factors among shooters

"The heinous crimes committed by Seung-Hui Cho were an unprecedented act of violence that no one could have foreseen, " Mr. Owczarski said.

WSJ: Virginia Tech Is Liable in Shootings

In the 2007 shootings at Virginia Tech, which resulted in the deaths of 33 people, gunman Seung-Hui Cho had been considered dangerous by a court and ordered to get outpatient treatment.

WSJ: Arizona Shooting Puts Focus on Gun Laws