A Port Authority police officer salutes during ceremonies marking the 10th anniversary of the 9/11 attacks on the World Trade Center in New York, Sept 11, 2011. [Photo/Agencies]

New York police, firefighters and Port Authority Police line up at one of the entrances of 9/11 Memorial Plaza before the tenth anniversary ceremonies at the World Trade Center site in New York, Sept 11, 2011. The 9/11 attacks changed life in the United States forever, but 10 years after the devastating hit, New Yorkers have learned to live in a more dangerous world and are ready to move on. [Photo/Agencies]