The city of New York has released thousands of fire department files from the attacks on the World Trade Center.
They include transmissions recorded on 11 September 2001 and testimonies from firefighters which were gathered later.
The city was forced to release the documents following a lawsuit filed by the New York Times, and supported by relatives of firefighters who died.
Records already published by the paper have raised questions whether some of the deaths might have been avoided.
More than 340 firefighters lost their lives on 11 September 2001. Many died after radio messages telling them to evacuate the north tower went unheard.
Last year a congressional inquiry into the attacks said there was a breakdown in communications between the emergency services.
The documents released on Friday include about 15 hours of radio communications between dispatchers and firefighters at the World Trade Center.
They also include more than 12,000 pages of individual oral histories compiled by the department in October 2001:
- A firefighter describes a woman leaping to her death from a tower and landing on a firefighter. "A lady in a blue dress came down. She went through the skylight and she hit this guy ... and she crushed him."
- "I'm trapped," says a civilian on a Fire Department radio dispatch tape. "I can't breathe much longer. Save me. I don't have much air. Please help me. I can barely breathe."
- A firefighter sees people falling from the twin towers. "I felt like I was intruding on a sacrament. They were choosing to die, and I was watching them and shouldn't have been, so me and another guy turned away and looked at the wall and we could still hear them hit."
- A rescuer expresses frustration with the co-ordination of the emergency operation. "I'm getting four different chiefs giving me four different command posts. ... Somebody at the scene has got to help me out and consolidate this."
The New York Times sought the records in 2002 under the Freedom of Information Act, and later sued the city when it refused to release them.
Earlier this year New York's highest court ordered that most - but not all - the documents should be made public.
The city has given several reasons for resisting the move - including concerns over interfering with the prosecution of 9/11 suspect Zacarias Moussaoui, and a confidentiality agreement with firefighters.
Some of the testimonies already leaked to the New York Times paint a picture of chaos and confusion on 11 September.
Firefighters recalled losing touch with one another and being unable to hear warnings about the imminent collapse of the north tower - the second of the two towers to fall.
Critics of the city's response - including relatives of those who died - hope the new documents will help them challenge the official conclusion that many firefighters heroically chose to ignore the warnings.