Here's what scientists know about mass school shootings

The three most deadly school shootings have occurred in the last decade.

Sheriff crime scene tape is seen outside of Robb Elementary School in Uvalde, Texas, as state troopers guard the area on May 24, 2022, after a mass school shooter killed 19 children and two teachers.
Sheriff crime scene tape is seen outside of Robb Elementary School in Uvalde, Texas, as state troopers guard the area on May 24, 2022, after a mass school shooter killed 19 children and two teachers.
(Image credit: ALLISON DINNER/AFP via Getty Images)

When the Columbine High School massacre took place in 1999 it was seen as a watershed moment in the United States — the worst mass shooting at a school in the country's history.

Now, it ranks fourth. The three school shootings to surpass its death toll of 13 — 12 students, one teacher — have all taken place within the last decade: 2012's Sandy Hook Elementary attack, in which a gunman killed 26 children and school staff; the 2018 shooting at Marjory Stoneman Douglas High School in Parkland, Florida, which claimed the lives of 17 people; and now the Robb Elementary School assault in Uvalde, Texas, where on May 24, 2022, at least 19 children and two adults were murdered.

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James Densley
Professor of Criminal Justice, Metropolitan State University

James Densley is a professor of Criminal Justice and Department Chair of the School of Law Enforcement and Criminal Justice at Metro State University, part of the Minnesota State system. He is the co-founder and co-president of The Violence Project Research Center, best known for its database of mass shooters. Densley has received global media attention for his work on street gangs, criminal networks, violence and policing. He is the author or co-author of seven books, including, "The Violence Project: How to Stop a Mass Shooting Epidemic," winner of the 2022 Minnesota Book Award; 50 peer-reviewed articles in leading social science journals; and over 100 book chapters, essays and other other works in outlets such as CNN, The Guardian, The LA Times, USA Today, The Wall Street Journal and The Washington Post.