The hijacked American Airlines plane crashed into the US military headquarters, killing 184 people. The jet hit the south-west side of the Pentagon, shortly after two other hijacked aeroplanes were flown into the twin towers of the World Trade Centre in New York.
The attack set off fires in a portion of the Pentagon and killed 125 people inside, in addition to those on board the plane.
"We fought hard to obtain this video because we felt that it was very important to complete the public record with respect to the terrorist attacks of September 11," the president of Judicial Watch, Tom Fitton, said.
The Flight 77 crash has spawned numerous conspiracy theories, including one from the French journalist Thierry Meyssam who suggested that a truck bomb or missile caused the explosion, not the plane. Most journalists, scientists and military experts have dismissed the conspiracy theories, but a minority of experts support them.