What we have learned, 20 years after Columbine

How are those closest to the Columbine school shooting observing its 20th anniversary? Coni Sanders’ father, David, was a teacher and coach at Columbine and the only adult killed -- but not before he warned hundreds of students to safety. David Cullen is a journalist who was at the scene. Lisa Desjardins talks to both of them about their memories of horror and how life has moved forward since.