One World Trade Center, left, now up to the 100th floor, and Four World Trade Center, right, overlook the ongoing construction of the site, Sunday, April 1, 2012 in New York. The unfinished One World Trade Center is one of the city’s tallest structures. If construction continues at its current pace, it will pass the Empire State Building this spring. Four WTC will top out at 72 floors. (AP Photo/Mark Lennihan).

A square pool, center, at the National September 11 Memorial is surrounded by ongoing construction, Sunday, April 1, 2012 at the World Trade Center in New York. The steel framework, lower left, for the Vehicle Security Center rises next to the excavated area, lower center, of the former Deutsche Bank building.