Newly released aerial photos of the World Trade Centre attack capture the towers' dramatic collapse, from just after the first fiery plane strike, to the apocalyptic dust clouds that spread over lower Manhattan.
The images were taken from a police helicopter - the only photographers allowed in the air space near the towers on September 11, 2001.
They were obtained by ABC News after it filed a Freedom of Information Act request last year with the National Institute of Standards and Technology, which investigated the collapse.
The chief curator of the planned September 11 museum, which is compiling a digital archive of attack coverage, said the still images are "a phenomenal body of work" that show a new, wide-angle look at the towers' collapse and the gray dust clouds that shrouded the city afterward.
The photos are "absolutely core to understanding the visual phenomena of what was happening," said Jan Ramirez, chief curator at the National September 11 Memorial & Museum.
The images of the dust clouds rising as high as some downtown skyscrapers "are some of the most exceptional images in the world, I think, of this event," Ramirez said.
ABC said the NIST gave the network 2779 pictures on nine CDs, saying some of the photographs had never been released before.
The network posted 12 photos this week on its website, all taken by ex-NYPD Aviation Unit Detective Greg Semendinger, who was first in the air in a search for survivors on the rooftop.
He said he and his pilot watched the second plane hit the south tower from the helicopter.
"We didn't find one single person. It was surreal," he told the Associated Press on Wednesday. "There was no sound. No sound whatsoever, but the noise of the radio and the helicopter. I just kept taking pictures."
He took three rolls of film with his Minolta camera, plus 245 digital shots. Semendinger said he gave the digital images to the 9/11 Commission and believes those images were released by the NSIT.
In the days after the attack, he emailed some of the photos to friends and several were posted on the internet.
Later, nine of the images were published in a book called "Above Hallowed Ground: A Photographic Record of September 11" without his consent. The book was a tribute to the officers who were killed that day.
The photos capture the enormous scope of the dust that enveloped the area.
In some images, the tops of the nearby Woolworth Building and other skyscrapers can be seen rising above the billowing dark plume against a clear blue sky. Buildings can hardly be seen at all in one image - just a burst of dust clouds hanging over the serene Hudson River at the southern tip of Manhattan.
A close-up image from earlier in the morning shows orange flames and black smoke rising past the antenna on top of the north tower, the first hit by a hijacked plane.
Ramirez said the museum, which is slated to open in 2012, saw a selection of the photos at police headquarters several years ago.
They are extremely important because the NYPD aviation unit had the clearance to be up in the air in lower Manhattan only "moments after the first tower was hit," and stayed in the area for the remainder of the day, she said.
Sometime after 10am, she said they were able to "predict that the north tower was going to fall." It did just before 10.30am.
The museum hopes to get a complete set of the photos.
"We've had our sights set on this body of visual evidence for several years," Ramirez said.
Semendinger retired from the NYPD in 2002 after 35 years, 20 of them in aviation. He said he has thought about publishing his work from those days.
"I almost didn't realise what I was seeing that day," he said. "Looking at it now it's amazing I took those pictures. The images are ... stunning."