New photographs of the attack on the World Trade Center in New York on 11 September 2001 have been published following a freedom of information request by ABC News.
ABC obtained a large number of pictures from the National Institute of Standards and Technology, which had collected them as part of its investigation into the events of that day.
This series of pictures was taken by Greg Semendinger of the New York Police Department from a helicopter over the city.
More than 3,000 people were killed in the airline attacks on the World Trade Center and the Pentagon, and in the crash of a fourth hijacked plane in Pennsylvania.
Both main towers of the World Trade Center collapsed following the attack, and the 7 World Trade Centre building. As the buildings fell, part of the city was enveloped in smoke, ash and debris.
The cloud continued to spread...
...and eventually engulfed a large area of Manhattan.
The huge scale of the disaster could be seen clearly from above.
As the cloud settled, a layer of ash covered every surface.
The day is now marked by an annual commemoration and a memorial is being constructed on the site of the World Trade Center's twin towers.
What are these?