Files released by Wikileaks have revealed that the United States believed many of those held at Guantanamo Bay were innocent or only low-level operatives.
The BBC reports the files, published in American and European newspapers, reveal analysis of all 780 people ever held at the facility.
The assessments show 220 people were classified as dangerous terrorists.
However, about 150 from Afghanistan and Pakistan were deemed innocent - with many detained for no apparent reason - while another 380 people were deemed to be low-ranking foot soldiers.
There are now just over 180 detainees at the US naval base in Cuba.
The Pentagon described the leak as "unfortunate" and described the assessments as snapshots that may now be outdated.
The BBC reports the files also detail plots again British and US targets.
The conspiracies, revealed under interrogation, included claims a nuclear weapon had been secreted in Europe for detonation should al-Qaeda chief Osama Bin laden be captured.
Other plots include plans to put cyanide into the air conditioning systems of US public buildings and attempts by al-Qaeda to recruit workers at London's Heathrow Airport.