Fifteen years after 9/11, many of the thousands of men and women who worked at the World Trade Center site are still coping with long-term health effects. Doctors and researchers continue investigating new health problems for responders, possibly due to exposure to toxins at Ground Zero, and how mental ailments like Post-Traumatic Stress Disorder may be contributing to physical complications. NewsHour Weekend Special Correspondent Karla Murthy reports on responders getting treatment and the doctors investigating these lingering health consequences.