On April 20, 1999, as two students carried out the deadly shooting at Columbine High School, senior Heather Martin was barricaded in a choir office with 60 other students. It would be several hours before emergency responders found the room and were able to help the group get out.
"I only saw the aftermath," she said. "I didn't see anything as it was happening." But she was shocked to later find out that the perpetrators were two of her peers, including one she had grown up with.