Columbine

In 1999, students, parents and educators were consumed with divergent explanations for the depravity of the shooting at Columbine High School in Littleton, Colorado.

Brian Groner, 27, has been charged with making a terroristic threat three months after he was first charged with the same crime because of statements he allegedly posted about the Columbine massacre.

"She appeared to have died from a self-inflicted wound," Dean Phillips, special agent in charge of the Denver field office of the FBI, confirmed.

The teens had created a hit list, researched bomb-making techniques and were hoarding weapons before their arrest.

As it was, the attackers took 13 precious lives, injured 24 other students and teachers, and left a scar in our nation's soul that remains with us still.

"School should not be a place where we have to worry about our kids getting killed. The more I see things like Parkland, I do get frustrated and feel sad that I failed."

Our kids go to school to learn math and science, not how to duck and cover.

The boy also set fire to the classroom before wounding himself.

"This time is different."

But for reasons police say we may never understand he decided to kill himself in school bathroom instead.

When professor Dorothy Espelage hears a school shooter was bullied, she asks, "What else?" 

Patrick Neville said some of his classmates may have survived if a member of staff had been armed.

'Well, I asked for it,' Manson says in Guardian interview about the backlash that followed his provocations.

Since the deadly events at Columbine High School in 1999, school shootings have become a disturbingly regular occurrence.

Below are some of the worst shooting incidents in recent years

He also wrote that Dylann Roof, the Charleston church shooter, sent him "over the top."

U.S. has less than five percent of world's population, but had 31 percent of mass shootings in 1966-2012.

A new book suggests kids know the games are a fantasy, even a healthy one.

Dr. Peter Langman's new book, released Friday, focuses on understanding for the sake of prevention.

A new play draws from the shooters' journals, letters and home videos to try to spur discussion about school violence. Some Columbine families are furious.

Susan Klebold to write about her son's actions and her involvement in suicide prevention