A firetruck, damaged in the attacks of September 11, 2001, is on display at the Sept. 11 museum. New York museum. (AP Photo) (Photo/Uncredited)
The entrance to the National September 11 Memorial Museum is shown. (AP Photo/Mark Lennihan) (Photo/Mark Lennihan)
The entrance to the National September 11 Memorial Museum is shown. (AP Photo/Mark Lennihan) (Photo/Justin Lane)
Members of the general public watch a screen projection of U.S. President Barack Obama. (AP Photo/Anthony Behar, Pool) (Photo/BEHAR ANTHONY)
Portraits of the Al-Qaeda hijackers are displayed at the National Sept. 11 Memorial Museum(AP Photo) (Photo/Uncredited)
The remains of New York City Fire Dept. truck from Engine Company 21 are displayed at the National Sept. 11 Memorial Museum,(AP Photo) (Photo/Uncredited)
Former New York City Mayor Rudolph Giuliani looks at displays at the National September 11 Memorial Museum (AP Photo/The Daily News, James Keivom, Pool) (Photo/James Keivom)
The Last Column was the final steel beam ceremonially removed from Ground Zero is shown at the dedication. (AP Photo/Timothy A. Clary, Pool) (Photo/TIMOTHY A. CLARY)
President Obama, Michelle Obama, Michael Bloomberg, Hillary Rodham Clinton, and Bill Clinton and tour the Sept. 11 museum. (AP Photo/Carolyn Kaster) (Photo/John Munson)
President Barack Obama speaks at the dedication ceremony for the National September 11 Memorial Museum on Thursday, May 15, 2014 (AP Photo/John Angelillo, Pool) (Photo/JOHN ANGELILLO)
An American Airlines slipper, an artifact from the Sept. 11, 2001 attacks, will be part of the National September 11 Memorial Museum. (AP Photo/Mark Lennihan, File) (Photo/Mark Lennihan)
A steel beam from the World Trade Center stands at the center of Foundation Hall on Thursday, May 15, 2014 (AP Photo/The Star-Ledger, John Munson, Pool) (Photo/John Munson)
A steel beam from the World Trade Center stands at the center of Foundation Hall on Thursday, May 15, 2014 (AP Photo) (Photo/JOHN ANGELILLO)
Fragments of the fuselage of Flight 11, that hit the World Trader Center, are displayed at the National Sept. 11 Memorial Museum. (AP Photo) (Photo/Uncredited)
The burn mask, right, of a World Trade Center survivor who was injured by burning jet fuel, is displayed at the National Sept. 11 Memorial Museum. (AP Photo) (Photo/Uncredited)
President Barack Obama speaks at the dedication ceremony for the National September 11 Memorial Museum on Thursday, May 15, 2014. (AP Photo/John Angelillo, Pool) (Photo/John Angelillo)
A woman cries at the National September 11 Memorial Museum in New York on Thursday, May 15, 2014. (AP Photo/Anthony Behar, Pool) (Photo/BEHAR ANTHONY)
A steel beam from the World Trade Center stands at the center of Foundation Hall on Thursday, May 15, 2014 (AP Photo/The Star-Ledger, John Munson, Pool) (Photo/Uncredited)
The twisted remains of a portion of the television transmission tower from the World Trade Center is displayed at the National Sept. 11 Memorial Museum. (AP Photo) (Photo/Uncredited)
President Obama, Michelle Obama, Michael Bloomberg, Hillary Rodham Clinton, and Bill Clinton and tour the Sept. 11 museum. (AP Photo/Carolyn Kaster) (Photo/Carolyn Kaster)
Steel from the World Trader Center north tower floors 97 and 98, left, is displayed at the National Sept. 11 Memorial Museum. (AP Photo) (Photo/Uncredited)
A two-inch thick World Trade Center steel column, that was bent into a horseshoe shape, and facade segment, are displayed at the National Sept. 11 Memorial Museum. (AP Photo) (Photo/Uncredited)
President Barack Obama and former New York City Mayor Michael Bloomberg at the September 11 Memorial Museum. (AP Photo/Carolyn Kaster) (Photo/Carolyn Kaster)