

A police officer stands watch at the Washington Monument as a flag flies at half-staff Sept. 12, 2001 in Washington, D.C. The city increased police presence around monuments and government buildings after the World Trade Center towers and the Pentagon were attacked by terrorists on Tuesday, Sept. 11, 2001. Andy Nelson/Staff
Hundreds participate in a candlelight vigil after walking to the White House from the National Mall and the US Capitol on Wednesday, Sept. 12, 2001, Across the United States, similar demonstrations were held to express solidarity after the attack on the World Trade Center towers and the Pentagon on Tuesday, Sept. 11, 2001. Andy Nelson/Staff
Zulema Barnes-Chung, 27, with her husband, Cleon Chung, holds a portrait of her mother, Sheila P. Barnes, in New York City on Sept. 14, 2001. Sheila worked on the 102nd floor of Tower #2, and went missing after the terrorist attack on Sept. 11, 2001. Melanie Stetson Freeman/Staff
New Yorkers write thoughts and prayers in chalk on the pavement in New York City's Union Square on Sept. 14, 2001. Melanie Stetson Freeman/Staff
New York Police and National Guard check identification before allowing workers into secured areas near the New York Stock Exchange on Sept. 17, 2001, almost a week after the terrorist attack on the World Trade Center. Melanie Stetson Freeman/Staff
A businessman heads to work in the financial district by the New York Stock Exchange on Sept. 17, 2001, wearing a mask due to the lingering ash and smoke from the World Trade Center collapse nearby. Melanie Stetson Freeman/Staff
Iron girders form a cross that has become a memorial at ground zero, the site of the twin towers of the World Trade Center, in New York City, on March 6, 2002. Andy Nelson/Staff
Workers sift through the rubble of the World Trade Center towers at ground zero in New York City March 6, 2002, nearly six months after their collapse. Andy Nelson/Staff
A small floral memorial is tacked to a post overlooking the pit at ground zero in New York City on March 6, 2002, where the terrorist attack caused the collapse of the World Trade Center towers. Andy Nelson/Staff
Tourists read picture books for sale about the World Trade Center tragedy. Vendors sell books, hats, T-shirts, crystals, and other items near the ground zero site in New York City on Sept. 5, 2003. Melanie Stetson Freeman/Staff
Workers are lowered along the outer wall of one of the World Financial Center buildings near the site of the World Trade Center towers in New York City Sept. 7, 2005. Andy Nelson/Staff
Members of the Port Authority Police Honor Guard salute during a wreath-laying ceremony at ground zero in New York City on Sept. 7. 2005. Andy Nelson/Staff
A group of business people view ground zero in New York City on Sept. 7, 2005, from the nearby Winter Garden. The Winter Garden was heavily damaged on Sept. 11, 2001. Andy Nelson/Staff
Visitors to ground zero react to an timeline photo exhibition during the fifth anniversary of the terrorist attack in New York City. Melanie Steteson Freeman/Staff
Family, friends, and co-workers of those that were lost in the terrorist attack on the World Trade Center towers listen to the names of the deceased read during New York City's commemoration ceremony in Zuccotti Park near ground zero on Sept. 11, 2010. Ann Hermes/Staff
Michka Peters pins a firefighter's badge on Zhanae Peters, 6, just before New York City's memorial service to commemorate the ninth anniversary of the terrorist attack on the World Trade Center towers near ground zero on Sept. 11, 2010. Ann Hermes/Staff
Canadian firefighter, Dave Arndt, left, and Marc DeLise, right, with the 'Road to Remember' fundraising project, salute during the national anthem at The New York City Fire Department Museum's memorial service for fallen firefighters on Sept. 11, 2010. Ann Hermes/Staff
Flags are flown at a rally to protest the proposed Muslim cultural center near ground zero on Sept. 11, 2010 on West Broadway in New York City. Ann Hermes/Staff
Victor Ortiz, Jr., 7, holds a image of his grandmother, Sonya, who was lost during the terrorist attack on the World Trade Center. The families who lost loved ones nine years ago attended a memorial service at Zuccotti Park near ground zero in New York City on Sept. 11, 2010. Ann Hermes/Staff
The Port Authority of New York and the New Jersey Police Department Pipes and Drums Band march down Church Street towards ground zero as protesters rally for and against the proposed Muslim cultural center in New York City's Financial District on Sept. 11, 2010. Ann Hermes/Staff
Nina Bolfing of Doylestown, Pa., listens to speakers during a rally against the proposed Muslim cultural center at 51 Park Place near ground zero in New York City on Sept. 11, 2010. Ann Hermes/Staff
Nathan Strauss Preparatory School of Humanities eighth graders, Melissa Urbano, left, Tatiana Harrison, center, and La-Starr Holmes, right, paint the school's playground in New York's Lower East Side as part of the September 11 National Day of Service. Ann Hermes/Staff
Tourists gather at the World Financial Building to see the progress on the memorial at the ground zero site in New York City on Sept. 11, 2010. Ann Hermes/Staff
Mourners walk through a meditation labyrinth at St. Paul's Chapel near ground zero during an all night vigil at sundown on Sept. 10, 2010. Ann Hermes/Staff
Patches, pins and badges decorate a religious vestment at St. Paul's Chapel which has become a museum and memorial to the 9/11 terrorist attack on the World Trade Center towers near the chapel. Ann Hermes/Staff
Amos Farooqui, left, and Bill Salter, right, light candles at a vigil in support of the proposed Muslim cultural center near ground zero on Sept. 10, 2010 in New York City. Ann Hermes/Staff
Two beams of light shine from the ground zero site in New York City's financial district on Sept. 10, 2010 in commemoration of the ninth anniversary of the terrorist attack on the World Trade Center towers. Ann Hermes/Staff