The CIA used a secret base at Guantanamo Bay, nicknamed Penny Lane, to turn some of al-Qaeda's most dangerous terrorists into double agents, US officials have admitted.
Inmates languishing under the camp's harsh regime were offered cash rewards, hotel-style rooms and even pornography if they agreed to help the CIA track down and kill fellow al-Qaeda operatives.
Instead of Guantanamo's spartan cells, they would be transferred to cottages equipped with private kitchens, showers and televisions, as well as their own patio.
A handful then signed agreements to work for the CIA, under which they were released and told to hook up once more with their former comrades. The programme, set up when President George W. Bush was in the White House, was potentially a huge gamble for the CIA, because of the risks the "turned" inmates would simply rejoin al-Qaeda's ranks.
There were also fears that they might pass on false information to provoke inaccurate drone strikes on civilians in al-Qaeda strongholds in Afghanistan and Yemen.