Today marks the 15th anniversary of the September 11, 2001 terror attacks. Nearly 3,000 people died that day at Ground Zero in New York City, where the Twin Towers collapsed. In the days that followed, Martha Teichner logged several reports from the area. She recently returned to lower Manhattan to visit the memorial built there, the people who return to commemorate lives lost, and the rebirth of a site that is hallowed ground.