The number of people that died was more than any other mass shooting in modern U.S. history up until the 2017 Las Vegas shooting. Before then, the deadliest campus shooting in United States history was in 1966 at the University of Texas, where Charles Whitman climbed to the 28th-floor observation deck of a clock tower and opened fire, killing 16 people before he was gunned down by police. In the Columbine High attack in 1999, two teenagers killed 12 fellow students and a teacher before killing themselves.