WATCH: Columbine Author on Myths, Lessons, and Warning Signs of Violence

Dave Cullen is a journalist and author who has been covering school shootings in America for two decades, starting with the mass shooting at Columbine High School in Littleton, Colo., in 1999, and later, writing about the massacre at Marjory Stoneman Douglas High School in Parkland, Fla., in his book “Parkland: The Birth of a Movement.”

Education Week senior staff writer Evie Blad spoke to Cullen on how the shooting at Columbine High shattered the notion of safety at schools and about how educators, law enforcement, and American society is still grappling with its lessons 25 years later.