When two gunmen opened fire at Columbine High School 20 years ago, Principal Frank DeAngelis didn't hesitate. "I saw the gunman but I also saw my kids," he told Inside Edition. "People ask me, 'Frank, why did you run towards the gunman?' and I say, 'Because I had to save my kids.'" DeAngelis hopes sharing his story will inspire others in need of healing. He has written a book, "They Call Me 'Mr. De': The Story of Columbine's Heart, Resilience and Recovery." All proceeds go to charity.