Scott Brian Larsen thinks every day about his father, Scott Andrew Larsen, a firefighter who lost his life responding to the Sept. 11th attacks in New York City. He is now a living tribute, working in the same firehouse as his dad. “Great men have walked this place,” Larson said, “I can continue on his legacy, and I try to do the best I can every day and, hopefully, will make him proud.” Diane Sawyer speaks with families about their lives 20 years after the tragedy during a special ABC 20/20 air