Chilling aerial photos of 9/11 attack released

The images were taken from a police helicopter -- the only photographers allowed in the airspace near the skyscrapers on Sept. 11, 2001. They were obtained by ABC after it filed a Freedom of Information Act request last year with the National Institute of Standards and Technology, the federal agency that investigated the collapse.

The chief curator of the planned Sept. 11 museum pronounced the pictures "a phenomenal body of work."

The photos are "absolutely core to understanding the visual phenomena of what was happening," said Jan Ramirez of the National September 11 Memorial & Museum. They are "some of the most exceptional images in the world, I think, of this event."

In some of the pictures, the tops of the nearby Woolworth Building and other skyscrapers can just be seen above the enormous cloud of debris, gray against a clear blue sky. Gray clouds billow through the streets of the financial district and shroud the 16 acres where the towers had stood just moments before.

Buildings can hardly be seen at all in one image -- just dust clouds hanging over the Hudson River at the southern tip of Manhattan.

One close-up shows orange flames and black smoke pouring from the upper floors of the north tower, the first hit by a hijacked plane.