WASHINGTON — A few hundred yards from the administrative offices of the Guantanamo Bay prison, hidden behind a ridge covered in thick scrub and cactus, sits a closely held secret.

A dirt road winds its way to a clearing where eight small cottages sit in two rows of four. They have long been abandoned. The special detachment of Marines that once provided security is gone.

But in the early years after 9/11, these cottages were part of a covert CIA program. Its secrecy has outlasted black prisons, waterboarding and rendition.

In these buildings, CIA officers turned terrorists into double agents and sent them home.

It was a risky gamble. If it worked, their agents might help the CIA find terrorist leaders to kill with drones. But 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, it was one of the many secret trade-offs the government made on its behalf. At the same time the government used the threat of terrorism to justify imprisoning people indefinitely, it was releasing dangerous people from prison to work for the CIA.

Nearly a dozen current and former U.S officials described aspects of the program to The Associated Press. All spoke on condition of anonymity because they were not authorized to publicly discuss the secret program, even though it ended in about 2006.

The program and the handful of men who passed through these cottages had various official CIA codenames. But those who were aware of the cluster of cottages knew it best by its sobriquet: Penny Lane.

It was a nod to the classic Beatles song and a riff on the CIA’s other secret facility at Guantanamo Bay, a prison known as Strawberry Fields.

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

When prisoners began streaming into the prison on the U.S. naval base at Guantanamo Bay, Cuba, in January 2002, the CIA recognized it as an unprecedented opportunity to identify sources. That year, 632 detainees arrived at the island. The following year 117 more arrived.

“Of course that would be an objective,” said Emile Nakhleh, a former top CIA analyst who spent time in 2002 assessing detainees but who did not discuss Penny Lane. “It’s the job of intelligence to recruit sources.”

By early 2003, Penny Lane was open for business.

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

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 collectively as the Marriott.

Current and former officials said dozens of prisoners were evaluated but only a handful, from varying countries, were turned into spies who signed agreements to spy for the CIA.

CIA spokesman Dean Boyd declined to comment.

Sen. Kelly Ayotte, R-N.H., who serves on the Armed Services and Homeland Security oversight committees, said Tuesday that she was still learning more about the program but was concerned about the numbers of prisoners who were released by the Bush and Obama administrations and returned to fight with terrorists against U.S. interests.

“So, when I juxtapose that to the CIA actually thinking that they can convert these people, I think it was very ill-conceived program for them to think that,” Ayotte said on MSNBC’s “Andrea Mitchell Reports. “These are some very hard-core individuals and many whom have been released by both administrations have gotten back in to fight us and our allies, unfortunately.”

Appearing on the program with Ayotte, Sen. Bob Casey, D-Pa., said it was difficult for him to evaluate the CIA program’s effectiveness. “But it has a degree of recklessness to it that I would be very concerned about,” Casey said.

The U.S. government says it has confirmed about 16 percent of former Guantanamo Bay detainees rejoin the fight against America. Officials suspect but have not confirmed that another 12 percent rejoined.

Though the number of double agents recruited through Penny Lane was small, the program was significant enough to draw keen attention from President George W. Bush, one former official said. Bush personally interviewed a junior CIA case officer who had just returned home from Afghanistan, where the agency typically met with the agents.

President Barack Obama took an interest the program for a different reason. Shortly after taking office, 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. So 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.

From what the Bush administration was saying about Guantanamo Bay prisoners at the time, the CIA would have seemingly had a large pool to draw from.

Vice President Dick Cheney called the prisoners “the worst of a very bad lot.” Defense Secretary Donald Rumsfeld said they were “among the most dangerous, best trained, vicious killers on the face of the Earth.”

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 Guantanamo Bay, more than three-fourths have been released, mostly during the Bush administration.

Many others remain at Guantanamo Bay, having been cleared for release by the military but with no hope for 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 Guantanamo.

But Remes, who was not aware of Penny Lane, said he understands 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 cooperate for a variety of reasons, officials said. Some received assurances that the U.S. 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 cooperate after the CIA insinuated it would harm his children, a former official said, harkening to similar threats interrogators lodged against admitted 9/11 mastermind Khalid Sheikh Mohammed.

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’d been on the CIA payroll.

Al-Qaida suspected the CIA would attempt a program like this and its operatives have been very suspicious of former Guantanamo Bay detainees, intelligence officials and experts said.

In one case, a former official recalled, al-Qaida came close to discovering one of the double agents in its midst.

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

Another former senior intelligence official said that never happened.

Officials said the program ended in 2006, as the flow of detainees to Guantanamo Bay slowed to a trickle. The last prisoner arrived there in 2008.

Penny Lane still stands and can be seen in satellite photos. The complex is surrounded by two fences and hidden among the trees and shrubs of Guantanamo Bay.