Members of the New York Police Department, Fire Department of New York and Port Authority of New York and New Jersey Police Department carry an American flag at the beginning of the memorial observances on the 13th anniversary of the Sept. 11 terror attacks on the World Trade Center in New York, Thursday, Sept. 11, 2014.   In New York, family members of those killed at the World Trade Center will read the names of the victims at a ceremony at ground zero. (AP Photo/Andrew Burton, Pool)

Photos: Nation remembers 9-11

The nation pauses Thursday to mark the thirteenth anniversary of the Sept. 11, 2001 terror attack.

In this Sunday, Sept. 7, 2014 photo, 1 World Trade Center towers above the lower Manhattan skyline in New York. Thirteen years after 9/11 forever changed the New York skyline, officials say developments at the World Trade Center are on track and on budget. (AP Photo/Mark Lennihan)

Photos: World Trade Center

Thirteen years after 9/11 forever changed the New York skyline, officials say developments at the World Trade Center are on track and on bud…