Saturday marks 20 years since 12 students and a teacher were gunned down at Columbine High School. It was the worst school shooting at the time.

A young Florida woman who traveled to Colorado and bought a shotgun for what authorities feared would be a Columbine-inspired attack just days ahead of the 20th anniversary was found dead Wednesday in an apparent suicide after a nearly 24-hour manhunt.

Even with the knowledge of being punished for skipping school, Hoggard High School students took part in a nationally planned school walk out.

Sue Klebold, the mother of Columbine killer Dylan Klebold, told ABC News' Diane Sawyer that when the Columbine tragedy happened, she couldn’t stop thinking about the victims and their families.

The father of a Columbine victim is speaking out about mental illness awareness and violence.