Mason is a student at Sparks Middle School. He was there Monday morning, waiting for the first bell, when he heard gunfire. Then he saw his friend, a classmate, coming toward him carrying a nine-millimeter pistol.  Seconds later, Mason was shot in his stomache. Today, as he heals, he is telling his story to Stephanie Elam.

A community is struggling to come to terms with the deadly shooting at a middle school in Sparks, Nevada, where a student shot and killed a teacher and wounded two students before taking his own life. Now, newly-released 911 recordings are shedding new light on those chaotic moments, and a hero emerges. Stephanie Elam reports.