WASHINGTON (AP) — A white, unmarked Boeing 737 landed in Guantanamo Bay, Cuba, before dawn on a CIA mission so secretive, many in the nation’s war on terrorism were kept in the dark.

Four of the nation’s most highly valued terrorist prisoners were aboard.

They arrived at Guantanamo on Sept. 24, 2003, years earlier than the U.S. has ever disclosed. Then, months later, they were just as quietly whisked away before the Supreme Court could give them access to lawyers.

The transfer allowed the U.S. to interrogate the detainees in CIA “black sites” for two more years without allowing them to speak with attorneys or human rights observers or challenge their detention in U.S. courts. Had they remained at the Guantanamo Bay prison for just three more months, they would have been afforded those rights.

“This was all just a shell game to hide detainees from the courts,” said Jonathan Hafetz, a Seton Hall University law professor who has represented several detainees.

Removing them from Guantanamo Bay underscores how worried President George W. Bush’s administration was that the Supreme Court might lift the veil of secrecy on the detention program. It also shows how insistent the Bush administration was that terrorists must be held outside the U.S. court system.

Years later, the program’s legacy continues to complicate President Barack Obama’s efforts to prosecute the terrorists behind the Sept. 11, 2001, attacks.

The arrival and speedy departure from Guantanamo were pieced together by The Associated Press using flight records and interviews with current and former U.S. officials and others familiar with the CIA’s detention program. All spoke on condition of anonymity to discuss the program.

Top officials at the White House, Justice Department, Pentagon and CIA consulted on the prisoner transfer, officials said.

“The so-called black sites and enhanced interrogation methods, which were administered on the basis of guidance from the Department of Justice, are a thing of the past,” CIA spokesman George Little said.

The American Civil Liberties Union renewed its call for a broad criminal investigation into the detention program Friday.

“Secret detention constitutes a grave breach of the Geneva Conventions, and the officials who authorized the CIA’s secret prisons and torture program should be held accountable,” Jameel Jaffer, the ACLU’s deputy legal director said.

At least four admitted al-Qaida operatives, some of the CIA’s biggest captures to date, were on the plane to Guantanamo: Abu Zubaydah, Abd al-Nashiri, Ramzi Binalshibh and Mustafa al-Hawsawi.

Binalshibh and al-Hawsawi helped plan the 9/11 attacks. Al-Nashiri was the mastermind of the 2000 bombing of the USS Cole. Zubaydah was an al-Qaida travel facilitator. They had spent months overseas enduring some of the harshest interrogation tactics in U.S. history.

By late summer 2003, the CIA believed the men had revealed their best secrets. The agency needed somewhere to hold them, but no longer needed to conduct prolonged interrogations.

The U.S. naval facility at Guantanamo Bay seemed a good fit. Bush had selected the first six people to face military tribunals there, and a federal appeals court unanimously ruled that detainees could not use U.S. courts to challenge their imprisonment.

And the CIA had just constructed a new facility, which would become known as Strawberry Fields, separate from the main prison at Guantanamo Bay.

The agency’s overseas prison network, meanwhile, was in flux. A jail in Thailand known as Cat’s Eye closed in December 2002, and in the fall of 2003 the CIA was preparing to shutter its facility in Poland and open a new one in Romania. Human rights investigators and journalists were asking questions. The CIA needed to reshuffle its prisoners.

The prisoner transfer flight, outlined in documents and interviews, visited five CIA prisons in Afghanistan, Poland, Romania, Morocco and Guantanamo Bay. The flight plan was so poorly thought out, some in the CIA derisively compared it to a five-card straight revealing the program to outsiders: Five stops, five secret facilities, all documented.

The flight logs were compiled by European authorities investigating the CIA program.

The flight started in Kabul, where the CIA picked up al-Hawsawi at the secret prison known as the Salt Pit. The Boeing 737 then flew to Szymany, Poland, where a CIA team picked up professed 9/11 mastermind Khalid Sheikh Mohammed and took him to Bucharest, Romania, to the new prison, code-named Britelite.

Next it was on to Rabat, Morocco, where the Moroccans ran an interrogation facility used by the CIA.

At 8:10 p.m. on Sept. 23, 2003, the Boeing 737 took off from a runway in Rabat. On board were al-Hawsawi, al-Nashiri, Zubaydah and Binalshibh. At 1 a.m. the following day, the plane touched down at Guantanamo.

The existence of a CIA prison at Guantanamo was reported in 2004, but it has always been unclear who was there. Unlike the overseas black sites, there was no waterboarding or other harsh interrogation tactics at Strawberry Fields, officials said. It was a holding facility, a place for some of the key figures in the 9/11 attacks to await trial.

Not long after they arrived, things began unraveling. In November, over the administration’s objections, the Supreme Court agreed to consider whether Guantanamo Bay detainees could sue in U.S. courts.

The administration had worried for several years that this might happen. In 2001, Justice Department lawyers Patrick Philbin and John Yoo wrote a memo saying courts were unlikely to grant detainees such rights. But if it happened, they warned, prisoners could argue that the U.S. had mistreated them and that the military tribunal system was unlawful.

“There was obviously a fear that everything that had been done to them might come out,” said al-Nashiri’s lawyer, Nancy Hollander.

Worse for the CIA, if the Supreme Court granted detainees rights, the entire covert program was at risk. Zubaydah and al-Nashiri could tell their lawyers about being waterboarded in Thailand. Al-Nashiri might discuss having a drill and an unloaded gun put to his head at a CIA prison in Poland.

“Anything that could expose these detainees to individuals outside the government was a nonstarter,” one U.S. official familiar with the program said, speaking on condition of anonymity to discuss the government’s legal analysis.

In early March 2004, as the legal documents piled up at the Supreme Court, the high court announced that oral arguments would be held in April. After that, a ruling could come at any time, and everyone at the island prison — secretly or not — would be covered.

On March 27, just as the sun was setting on Guantanamo, a Gulfstream IV jet left Cuba. The plane landed in Rabat the next morning. By the time the Supreme Court ruled June 28 that detainees should have access to U.S. courts, the CIA had once again scattered Zubaydah, al-Nashiri and the others throughout the black sites.

Two years later, after The Washington Post revealed the existence of the program, Bush emptied the prison network. Fourteen men, including the four who had been at Guantanamo Bay years earlier, were moved to the island prison. They have remained there ever since.

The four men who were making their second journey to Guantanamo Bay received what they nearly obtained years earlier, before they were spirited away.

“The International Committee of the Red Cross is being advised of their detention and will have the opportunity to meet with them,” Bush said in a White House speech Sept. 6, 2006. “Those charged with crimes will be given access to attorneys who will help them prepare their defense, and they will be presumed innocent.”