These images were first released in 2010 after a FOIA request.
After 9/11 the U.S.'s National Institute of Standards and Technology collected images from amateur, professional and freelance photographers as part of its investigation into the collapse of the World Trade Centre. It completed its research in 2005.
In the summer of last year, ABC asked NIST to release the images and filed a request under the Freedom of Information Act for access to them.
The images seen here are ones taken by NYPD helicopters and come from the 2,779 pictures supplied on nine CDs to the news organisation.