Landov9/11 Memorial Ceremony09.11.11 9:00 PM ETLandovLandovSaluteNew York City Police Officer Danny Shea, a military vet, salutes at the north pool. Pablo Martinez Monsivais / AP PhotoObama Sept 11President Barack Obama and first lady Michelle Obama former President George W. Bush and former first lady Laura Bush visit North Memorial Pond at the National Sept. 11th Memorial Sunday, Sept., 11, 2011, in New York. Getty ImagesThe President RemembersPresident Obama and First Lady Michelle Obama at the north pool. Mladen Antonov / AFP / Getty ImagesStars and StripesA U.S. flag recovered from the 9/11 attacks is displayed by New York City police officers and firefighters. Brian Snyder / LandovSide by SidePresident Obama, First Lady Michelle Obama, former president George W. Bush, and former first lady Laura Bush stand beneath a display marking the moment when American Flight 11 hit the North Tower of the World Trade Center. Timothy A. Clary / AP PhotoTen Years Later, on AlertSecret Service snipers keep watch from the roof of the September 11 Memorial Museum. David Handschuh / Getty ImagesGrieving TogetherPresident Obama and First Lady Michelle Obama greet mourners. Brian Snyder / LandovIn MemoriamCellist Yo-Yo Ma plays during ceremonies. Timothy A. Clary / AP PhotoIn MourningA woman cries over a name on the edge of the south pool. Mary Altaffer / AP PhotoFormer New York City Mayor Rudy GiulianiFormer New York City Mayor Rudy Giuliani and his wife Judith Nathan pay their respects at the north reflection pool near the bronze-etched names of the victims of the 9/11 terrorist attack on the National September 11 Memorial during a ceremony marking the 10th anniversary of the attacks at World Trade Center, Sunday, Sept. 11, 2011 in New York.Jason DeCrow / AP ImagesSept 11 10th AnniversaryFamily members of victims of 9/11 read the names of those killed in the attack Sunday, Sept. 11, 2011, during a ceremony marking the 10th anniversary of the attacks at the National September 11 Memorial at the World Trade Center site in New York. Getty Images September 11, 2011At the memorial pool, Vasantha Velamuri mourns at the sight of her husband's name, Sankara Sastry Velamuri, who died in the World Trade Center, during ceremonies at the World Trade Center site September 11, 2011 in New York City.