On April 20, 1999, people across the country and the world were shocked by the news that two gunmen had opened fire in Columbine High School in Colorado, killing 15 and injuring two dozen more. This was one of the first times many Americans heard the phrase “mass shooting.”
The Congressional Research Service defines mass shootings as incidents in which at least five people are killed with a firearm “within one event, and in one or more locations in close proximity.”
Since Columbine, mass shootings “continue to increase in both number and scope,” according to The National Criminal Justice Reference Service. From 1998-2007, there were 21 recorded mass shootings. From 2008-2017, that number jumped to 51 shootings — including the deadliest mass shooting in U.S. history, in which 58 people were killed at a Las Vegas music festival on Oct. 1, 2017.
Many of the deadliest mass shootings have been perpetrated by people who obtained their guns illegally — whether they bought them on the black market or took them from someone they knew who had legally purchased the weapons. This may explain why many of these shootings took place in the states with the strictest gun laws.
Mass shootings account for just a small fraction of the number of Americans killed by guns each year, whether it is a homicide or a suicide. In 2017, there were 12 firearm-related deaths for every 100,000 people in the United States. In the cities with the most gun violence, that rate was over 20 per 100,000.
There has been relatively little legislative action taken at the federal level in response to mass shootings over the past 20 years. Most recently, the Trump Administration’s Justice Department ruled in 2018 that an existing ban on fully automatic rifles extends to bump stocks — an attachment used by the Las Vegas shooter that makes semi-automatic rifles function like automatic ones.
To identify the deadliest mass shootings since Columbine, 24/7 Wall St. reviewed the number of fatalities from mass shootings that occurred after April 20, 1999 recorded by the Congressional Research Service, the FBI, the Washington Post, and other sources. Shooters who were killed as a result of suicide or in shootouts with police were not included in the fatality count. Spree shootings that take place in multiple locations with four or fewer people killed in a single location were not considered. Shootings that were a single domestic incident were also not considered.