Visitors to the National September 11 Memorial walk below the rising towers 1 World Trade Center, left, and 4 World Trade Center, Monday, Sept. 10, 2012 in New York. Tuesday will mark the eleventh anniversary of the attacks of Sept. 11, 2001. (AP Photo/Mark Lennihan)

Photos of victims of the attacks of September 11, and messages from their loved ones, are shown at a news conference, Monday, Sept. 10, 2012 in New York. On the eve of the Sept. 11 anniversary, the faces and recorded voices of those who died have been unveiled as part of the future 9/11 Memorial Museum. (AP Photo/Mark Lennihan)

Photos of victims of the attacks of September 11 and messages from their loved ones, are shown at a news conference, Monday, Sept. 10, 2012 in New York. On the eve of the Sept. 11 anniversary, the faces and recorded voices of those who died have been unveiled as part of the future 9/11 Memorial Museum. (AP Photo/Mark Lennihan)

Jessica Huynh, top, and Alana Roecker brush in the colors of a paint-by-number canvas of the original World Trade Center towers, at a news conference, Monday, Sept. 10, 2012 in New York. On the eve of the Sept. 11 anniversary, the faces and recorded voices of those who died have been unveiled as part of the future 9/11 Memorial Museum. (AP Photo/Mark Lennihan)

Electronic images of victims of the attacks of Sept. 11, 2001, part of a future touch-screen display, are shown during a news conference, Monday, Sept. 10, 2012 in New York. On the eve of the Sept. 11 anniversary, the faces and recorded voices of those who died have been unveiled as part of the future 9/11 Memorial Museum. (AP Photo/Mark Lennihan)

FILE - In this file photo of Sept. 6, 2012, One World Trade Center, now up to 105 floors, rises above the National September 11 Memorial and Museum in New York. Eleven years after terrorists attacked the World Trade Center, the new World Trade Center now dominates the lower Manhattan skyline. (AP Photo/Mark Lennihan, File)

FILE - In this file photo of Jan. 27, 2010, an ironworker reaches for a beam suspended from a crane at One World Trade Center, in New York. Eleven years after terrorists attacked the World Trade Center, the new World Trade Center now dominates the lower Manhattan skyline. (AP Photo/Mark Lennihan, File)

FILE - In this file photo of March 23, 2012, ironworkers connect steel beams above the 93rd floor of One World Trade Center in New York. One World Trade Center, formerly known as the Freedom Tower, will open in 2014 on the northwest corner of the trade center site with 3 million square feet of office space. (AP Photo/Mark Lennihan, File)

In this Friday, Sept. 7, 2012 photo, an ironworker watches as a crane lifts a load of construction supplies at the World Trade Center transportation hub, in New York. The new transportation hub at the trade center will connect 13 subway lines and PATH trains to New Jersey when it opens in 2015. (AP Photo/Mark Lennihan)

FILE - In this file photo of Aug. 2, 2012, Billy Geoghan, center, follows fellow ironworker James Brady up a ladder to the 104th floor of One World Trade Center in New York. One World Trade Center, formerly known as the Freedom Tower, will open in 2014 on the northwest corner of the trade center site with 3 million square feet of office space. (AP Photo/Mark Lennihan, File)

In this Friday, Sept. 7, 2012 photo, an ironworker watches as a crane begins to lift a load of construction supplies at the World Trade Center transportation hub, Friday, Sept. 7, 2012, in New York. The new transportation hub at the trade center will connect 13 subway lines and PATH trains to New Jersey when it opens in 2015. (AP Photo/Mark Lennihan)

FILE - In this April 17, 2012 file photo, One World Trade Center rises above the lower Manhattan skyline and the National September 11 Memorial and Museum, in New York. Eleven years after terrorists attacked the World Trade Center, the new World Trade Center now dominates the lower Manhattan skyline. (AP Photo/Mark Lennihan, File)

FILE - In this file photo of Sept. 6, 2012, One World Trade Center, now up to 105 floors, rises above the National September 11 Memorial and Museum in New York. Eleven years after terrorists attacked the World Trade Center, the new World Trade Center now dominates the lower Manhattan skyline. (AP Photo/Mark Lennihan, File)

FILE - In this file photo of June 23, 2012, construction cranes perch on top of One World Trade Center, left, and Four World Trade Center in New York. Eleven years after terrorists attacked the World Trade Center, the new World Trade Center now dominates the lower Manhattan skyline. (AP Photo/Mark Lennihan, File)