The president closed his eyes and clasped his hands at the outdoor memorial where the twin towers of the World Trade Center once dominated the Manhattan skyline. He shook hands with 9/11 family members and others dressed in black at the site where the skyscrapers were brought down by planes commandeered by bin Laden's followers. Nearly 3,000 people were killed.

The president met privately at the memorial site with about 60 family members from various 9/11 organizations. He also visited the firefighters and police officers whose response to the terror attacks of Sept. 11, 2001, turned them into heroes and symbols of national resolve, but also cost them heavy casualties on that horrific day.

"This is a symbolic site of the extraordinary sacrifice that was made on that terrible day," the president said at Engine 54, Ladder 4, Battalion 9. The firehouse in New York's theater district lost 15 firefighters on 9/11, more than any other firehouse.

Months before the 10th anniversary of Sept. 11, and days after bin Laden was killed in Pakistan by U.S. commandos, Obama's visit gave New York its own moment of justice. The day was one of sober remembrance, thanks given to firefighters, police and U.S. troops, and reminders of the challenges ahead and the president's call for addressing them with unity.