A non-profit government watchdog has succeeded in getting the US to release videotapes of a plane striking the Pentagon on 11 September 2001.
The impact caused a five-floor section of the building to collapse
The conservative group Judicial Watch filed a Freedom of Information Act request in December 2004, which was denied a month later, the group says.
The Pentagon said it could not release the videos in question because they were part of an ongoing investigation against al-Qaeda plotter Zacarias Moussaoui, according to Judicial Watch.
Judicial Watch sued the government over its refusal, saying there was "no legal basis" for it.
Government resistance collapsed after a court sentenced Moussaoui to life in prison for his role in the 9/11 attacks, and they agreed to release the video, a Judicial Watch spokeswoman told the BBC.
Judicial Watch describes itself as a conservative, non-partisan foundation that fights government corruption.
The organisation's president, Tom Fitton, said in a statement he hoped the release of the footage would "put to rest the conspiracy theories involving American Airlines 77", the plane that hit the Pentagon on 9/11.
His remark was apparently a reference to ideas aired in books such as Thierry Meyssan's The Pentagate, which argues that a missile, not a plane, struck the headquarters of the US defence department.
The French journalist and left-wing activist claims the US government itself was behind the attacks.
Two books he published on the subject were worldwide bestsellers.
A Pentagon spokesman, Glen Flood, said in 2002 Mr Meyssan's first book was "a slap in the face and real offence to the American people".