'How the Columbine shooting changed my life'
Twelve students and a teacher were killed in the massacre in Colorado on 20 April 1999. It shocked the nation.
Frank DeAngelis was the school principal. He begins each day by saying the names of the 13 victims.
Samantha Haviland was a student at the time, and still suffers from PTSD and survivor's guilt. She has a message for the growing number of school shooting survivors in the US.
Reporter: Nada Tawfik, producer: Ashley Semler, cameraman: Andrew Herbert.