Flowers lay at the base of the South Pool of the 9/11 Memorial before tenth anniversary ceremonies at the site of the World Trade Center September 11, 2011, in New York, USA. EPA/TODD HEISLER / POOL
United States President Barack Obama (R), First Lady Michelle Obama (2nd R) and former President George W. Bush (L) and wife Laura Bush walk past the North Pool of the 9/11 Memorial during tenth anniversary ceremonies at the site of the World Trade Center September 11, 2011, in New York, USA. EPA/JUSTIN LANE / POOL
US President Barack Obama (R), First Lady Michelle Obama, former US president Geore W. Bush and wife Laura Bush stand at the North Pool of the 9/11 Memorial during the tenth anniversary ceremonies at the site of the World Trade Center September 11, 2011, in New York. EPA/TIMOTHY A. CLARY / POOL
A police officer runs his hand along the names inscribed on the South Pool of the 9/11 Memorial before tenth anniversary ceremonies at the site of the World Trade Center September 11, 2011, in New York, USA. EPA/TODD HEISLER / POOL
A 9/11 Memorial worker cleans the bronze panels that bear the names of the victims around the perimeter of the North Pool of the memorial before the tenth anniversary ceremonies at the site of the World Trade Center September 11, 2011, in New York, USA. EPA/JEFFERSON SIEGEL / POOL
At dawn the North Pool of the 9/11 Memorial before the tenth anniversary ceremonies at the site of the World Trade Center September 11, 2011, in New York, USA. EPA/JEFFERSON SIEGEL / POOL
Flowers lay at the base of the South Pool of the 9/11 Memorial before tenth anniversary ceremonies at the site of the World Trade Center September 11, 2011, in New York, USA. EPA/TODD HEISLER / POOL
A 9/11 Memorial worker cleans the bronze panels that bear the names of the victims around the perimeter of the North Pool of the memorial before the tenth anniversary ceremonies at the site of the World Trade Center September 11, 2011, in New York, USA. EPA/JEFFERSON SIEGEL / POOL
At dawn the North Pool of the 9/11 Memorial before the tenth anniversary ceremonies at the site of the World Trade Center September 11, 2011, in New York, USA. EPA/JEFFERSON SIEGEL / POOL
US First Lady Michelle Obama (R) embraces victims' family members at the 9/11 Memorial during the tenth anniversary ceremonies at the site of the World Trade Center September 11, 2011, in New York, USA. EPA/CHIP SOMODEVILLA / POOL
United States President Barak Obama (R), first Lady Michelle Obama (2nd R) and former President George W. Bush (L) walk past the North Pool of the 9/11 Memorial during tenth anniversary ceremonies at the site of the World Trade Center September 11, 2011, in New York, USA. EPA/JUSTIN LANE / POOL
United States President Barack Obama (R), First Lady Michelle Obama (2nd R) and former President George W. Bush (L) and wife Laura Bush walk past the North Pool of the 9/11 Memorial during tenth anniversary ceremonies at the site of the World Trade Center September 11, 2011, in New York, USA. EPA/JUSTIN LANE / POOL
Police officers walk along the South Pool of the 9/11 Memorial before tenth anniversary ceremonies at the site of the World Trade Center September 11, 2011, in New York, USA. EPA/TODD HEISLER / POOL
US President Barack Obama (2nd R) embraces victims' family members as First Lady Michelle Obama (R) stands by at the 9/11 Memorial during the tenth anniversary ceremonies at the site of the World Trade Center September 11, 2011, in New York, USA. EPA/CHIP SOMODEVILLA / POOL
US President Barack Obama (2nd R) embraces victims' family members as First Lady Michelle Obama (R) stands by at the 9/11 Memorial during the tenth anniversary ceremonies at the site of the World Trade Center September 11, 2011, in New York, USA. EPA/CHIP SOMODEVILLA / POOL
US President Barack Obama (2nd R) embraces victims' family members as First Lady Michelle Obama (R) stands by at the 9/11 Memorial during the tenth anniversary ceremonies at the site of the World Trade Center September 11, 2011, in New York, USA. EPA/CHIP SOMODEVILLA / POOL
Former U.S. President George W. Bush (R) embraces victims' family members at the 9/11 Memorial during the tenth anniversary ceremonies at the site of the World Trade Center September 11, 2011, in New York, USA. EPA/CHIP SOMODEVILLA / POOL
Names of those killed on 9/11 are seen around a memorial pool at the National September 11 Memorial at the World Trade Center site in New York, USA, 11 September 2011. EPA/SETH WENIG / POOL
A memorial pool is seen at the National September 11 Memorial at the World Trade Center site in New York, USA, 11 September 2011. EPA/SETH WENIG / POOL
A sniper team works atop the September 11 Museum before the tenth anniversary ceremonies at the site of the World Trade Center September 11, 2011, in New York, USA. EPA/TODD HEISLER / POOL
US President Barack Obama (R), First Lady Michelle Obama, former US president Geore W. Bush and wife Laura Bush stand at the North Pool of the 9/11 Memorial during the tenth anniversary ceremonies at the site of the World Trade Center September 11, 2011, in New York. EPA/TIMOTHY A. CLARY / POOL
US President Barack Obama and First Lady Michelle Obama at the North pool of the 9/11 Memorial during the tenth anniversary ceremonies at the site of the World Trade Center September 11, 2011, in New York, USA. EPA/DAVID HANDSCHUH / POOL
New York police and firefighters and Port Authority Police line up at one of the entrances of the 9/11 Memorial Plaza before the tenth anniversary ceremonies at the site of the World Trade Center September 11, 2011, in New York, USA. EPA/AARON SHOWALTER / POOL
A general view at dawn of the 9/11 Memorial at the Pentagon before the 10th Anniversary 9/11 Remembrance Ceremony in Arlington, Virginia, USA, 11 September 2011. EPA/MICHAEL REYNOLDS
A New York City police department officer looks out over the North Pool of the 9/11 Memorial during tenth anniversary ceremonies at the site of the World Trade Center September 11, 2011, in New York, USA. EPA/JUSTIN LANE / POOL
