On April 20, 1999 Eric Harris and Dylan Klebold, opened fire on students at at Columbine High, killing a dozen students and a teacher and causing injury to two dozen others before taking their ownlives.
On December 14, 2012, twenty first graders and six adults were shot and killed during the Sandy Hook Elementary School shooting. A lone perpetrator forced his way into the school and began shooting at children and faculty before police arrived and he turned the gun on himself.
On June 12, 2016, Omar Mateen, a 29-year-old security guard, killed 49 people and wounded 53 others in a terrorist attack/hate crime inside Pulse, a gay nightclub in Orlando, Florida.
On the night of October 1, 2017, a gunman opened fire on a crowd of concertgoers at the Route 91 Harvest music festival on the Las Vegas Strip in Nevada, leaving 58 people dead and 546 injured.