Firefighters tell their stories of loss on 9/11, the rise of the Freedom Tower

In the year following 9/11, Ted Koppel interviewed four firefighters who were on top of the rubble of the World Trade Center, all of whom lost their sons after 9/11. We spoke with those four firefighters again in 2010 as they continued to honor their sons' legacies. This week, Nightline is remembering those brave men as the nation pays tribute.