Florida school shooting survivor describes traumatic day

In the wake of the last week's high school shooting in Florida, American gun laws are under fire from survivors of the massacre. Rising from the shock and horror of the shooting, in which 17 students were killed, is a survivor-led campaign to tighten gun laws. A march on Washington is being organised for March 24. One of the founding members of the #neveragain movement is Alfonso Calderon, he's a 16-year-old student at the school and survived the massacre by hiding in a closet with classmates for three hours. He tells Susie Ferguson about the traumatic experience.