Judy Goos, left, hugs her daughter's friend, Isaiah Bow, 20, an eyewitnesses, as Terrell Wallin, 20, right, looks on, outside Gateway High School where witnesses were brought for questioning after a gunman opened fire at the midnight premiere of the "Dark Knight Rises" movie in Aurora, Colo.

Associated Press/July 2012

A man wipes away tears outside a Sikh temple in Oak Creek, Wis. after a shooting. A white supremacist killed six worshippers and injured four other people before taking his own life.

Associated Press/August 2012

Smoke rises from a sniper's gun as he fires from the tower of the University of Texas administration building in Austin, Texas at people below. Grant Duwe, a criminologist with the Minnesota Department of Corrections, says, "Mass shootings provoke instant debates about violence and guns and mental health and that's been the case since Charles Whitman climbed the tower at the University of Texas in 1966." The engineering student and former Marine killed 13 people and an unborn child and wounded 32 others in the shooting.

Associated Press/August 1966