In the early years after 9/11, the CIA turned some Guantánamo Bay prisoners into double agents then sent them home to help the US kill terrorists, current and former US officials said.

The CIA promised the prisoners freedom, safety for their families, and millions of dollars from secret accounts.

It was a risky gamble. Officials knew there was a chance that some prisoners might quickly spurn their deal and kill Americans. For the CIA, that was an acceptable risk in a dangerous business. For the American public, which was never told, the programme was one of the many secret trade-offs the government made on its behalf. At the same time the government used the fear of terrorism to justify jailing people indefinitely, it was releasing dangerous people to work for the CIA.

The programme was carried out in a secret facility built near the prison's administrative offices in Guantánamo Bay, Cuba. The eight small cottages were hidden behind a ridge covered in thick scrub and cactus.

The programme and the handful of men who passed through these cottages had various official CIA codenames.

But those aware of the cottages knew it best by its sobriquet, Penny Lane, a nod to the Beatles song and a riff on the CIA's other secret facility at Guantánamo, a prison known as Strawberry Fields.

Nearly a dozen current and former US officials described aspects of the programme. All spoke on condition of anonymity as no one was authorised to discuss the secret programme publicly by name, even though it ended in about 2006.

Some of the men who passed through Penny Lane helped the CIA find and kill many top al-Qaida operatives, current and former US officials said. Others stopped providing useful information and the CIA lost touch with them.

When prisoners began streaming into Guantánamo Bay in January 2002, the CIA recognised it as an unprecedented opportunity to identify sources. That year, 632 detainees arrived at the detention centre. The following year a further 117 arrived.

By early 2003, Penny Lane was open for business.

Candidates were ushered from prison to the relative comfort of Penny Lane, officials said. The cottages had private kitchens, showers and televisions. Each had a patio.

Real beds



Some prisoners asked for, and received, pornography. One official said the biggest luxury in each cottage was the bed – not a military-issued cot but a real bed with a mattress. The cottages were designed to feel more like hotel rooms than prison cells, and some CIA officials jokingly referred to them as the Marriott.

Current and former officials said dozens of prisoners were evaluated but only a handful, from a variety of countries, were turned into spies who agreed to work for the CIA.

The CIA declined to comment on the claims.

The US government says it has confirmed that about 16% of former Guantánamo Bay detainees rejoined the fight against America. Officials suspect, but have not confirmed, that a further 12% also took up arms against the US.

It's not clear whether the men from Penny Lane are included in those figuresNone of the officials interviewed by the AP knew of an instance in which any double agent killed Americans.

Though the number of double agents recruited at Penny Lane was small, the programme was significant enough to draw President George Bush's attention, a former official said. Bush interviewed a junior CIA case officer who had just returned from Afghanistan, where the agency typically met with the agents.

President Barack Obama took an interest for a different reason. Shortly after taking office in 2009, he ordered a review of the former detainees working as double agents because they were providing information used in Predator drone strikes, one of the officials said.

Infiltrating al-Qaida has been one of the CIA's most sought-after but difficult goals, something that other foreign intelligence services have only occasionally accomplished. Candidates for Penny Lane needed legitimate terrorist connections. To be valuable to the CIA, the men had to be able to reconnect with al-Qaida.

The CIA would have seemingly had a large pool to draw from. Vice-President Dick Cheney called the Guantánamo prisoners "the worst of a very bad lot". The US defence secretary, Donald Rumsfeld, said they were "among the most dangerous, best trained, vicious killers on the face of the Earth".

Flimsy evidence



In reality, many were held on flimsy evidence and were of little use to the CIA. While the agency looked for viable candidates, those with no terrorism ties sat in limbo. It would take years before the majority of detainees were set free, having never been charged. Of the 779 people who were taken to Guantánamo, more than three-quarters have been released, mostly during the Bush administration.

Many others remain at Guantánamo Bay, having been cleared for release but with little hope of freedom in sight.

"I do see the irony on the surface of letting some really very bad guys go," said David Remes, an American lawyer who has represented about a dozen Yemeni detainees at Guantánamo. But Remes, who was not aware of Penny Lane, said he understood its attraction.

"The men we were sending back as agents were thought to be able to provide value to us," he said.

Prisoners agreed to co-operate for a variety of reasons, officials said. Some received assurances that the US would resettle their families. Another thought al-Qaida had perverted Islam and believed it was his duty as a Muslim to help the CIA destroy it. One detainee agreed to co-operate after the CIA insinuated it would harm his children, a former official said.

All were promised money. Exactly how much each was paid remains unclear. But altogether, the government paid millions of dollars for their services, officials said. The money came from a secret CIA account, codenamed Pledge, that's used to pay informants, officials said.

The arrangement led to strategic discussions inside the CIA: if the agency's drones had a shot at Osama bin Laden or his deputy, Ayman al-Zawahri, would officials take the shot if it meant killing a double agent on the American payroll? It never came to that.

The biggest fear, former officials involved with the program recalled, was that a former detainee would attack Americans then publicly announce that he had been on the CIA payroll.

Al-Qaida suspected the CIA would attempt a programme like this and its operatives were very suspicious of former Guantánamo detainees, intelligence officials and experts said.

The US government had such high hopes for Penny Lane that one former intelligence official recalled discussions about whether to secretly release a pair of Pakistani men into the US on student or business visas. The hope was that they would connect with al-Qaida and lead authorities to members of a US cell.

Another former senior intelligence official said that never happened.

Officials said the programme ended in 2006, as the flow of detainees to Guantánamo slowed to a trickle. The last prisoner arrived in 2008. Penny Lane still stands and can be seen in satellite photos, but the complex has long been abandoned.