On a cold day in early 2003, two senior CIA officers arrived at the U.S. Embassy in Warsaw to pick up a pair of large cardboard boxes. Inside were bundles of cash totaling $15 million that had been flown from Germany via diplomatic pouch.

The men put the boxes in a van and weaved through the Polish capital until coming to the headquarters of Polish intelligence. They were met by Col. ­Andrzej Derlatka, deputy chief of the intelligence service, and two of his associates.

The Americans and Poles then sealed an agreement that over the previous weeks had allowed the CIA the use of a secret prison — a remote villa in the Polish lake district — to interrogate al-Qaeda suspects. The Polish intelligence service received the money, and the CIA had a solid location for its newest covert operation, according to former agency officials who spoke on the condition of anonymity to discuss the interrogation program, including previously unreported details about the creation of the CIA’s “black sites,” or secret prisons.

The CIA prison in Poland was arguably the most important of all the black sites created by the agency after the Sept. 11, 2001, attacks. It was the first of a trio in Europe that housed the initial wave of accused Sept. 11 conspirators, and it was where Khalid Sheik Mohammed, the self-declared mastermind of the attacks, was waterboarded 183 times after his capture.

Much about the creation and operation of the CIA’s prison at a base in one of the young democracies of Central Europe remains cloaked in mystery, matters that the U.S. government has classified as state secrets. But what happened in Poland more than a decade ago continues to reverberate, and the bitter debate about the CIA’s interrogation program is about to be revisited.

The Senate Intelligence Committee intends to release portions of an exhaustive 6,000-page report on the interrogation program, its value in eliciting critical intelligence and whether Congress was misled about aspects of the program.

The treatment of detainees also continues to be a legal issue in the military trials of Mohammed and others at Guantanamo Bay in Cuba.

And in December, the European Court of Human Rights heard arguments that Poland violated international law and participated in torture by accommodating its American ally; a decision is expected this year.

“In the face of Polish and United States efforts to draw a veil over these abuses, the European Court of Human Rights now has an opportunity to break this conspiracy of silence and uphold the rule of law,” said Amrit Singh, a lawyer with the Open Society Justice Initiative, which petitioned the court on behalf of a detainee who was held at the Polish site.

Wanted: A better location

The story of a Polish villa that became the site of one of the most infamous prisons in U.S. history began in the Pakistani city of Faisalabad with the capture of Zayn al-Abidin Muhammed Hussein, better known as Abu Zubaida, in March 2002. The CIA needed a place to stash its first “high-value” detainee, a man who was thought to be closely tied to the al-Qaeda leadership and might know of follow-on plots.

Cambodia and Thailand offered to help the CIA. Cambodia turned out to be the less desirable of the two. Agency officers told superiors that a proposed site was infested with snakes. So the agency flew Abu Zubaida to Thailand, housing him at a remote location at least an hour’s drive from Bangkok.

The CIA declined to comment, as did Polish authorities through their country’s embassy in Washington. Derlatka, the Polish intelligence officer, did not return messages seeking comment.

Several months after the detention of Abu Zubaida, the CIA caught Abd al-Rahim al-Nashiri, suspected of ties to an al-Qaeda attack on a U.S. warship in Yemen. He, too, was taken to the Thai site.

With the prospect of holding more and more captives, the CIA required a better location. “It was just a chicken coop we remodeled,” a former senior agency official said of the facility in Thailand.

The CIA reached out to foreign intelligence services. The agency’s station chief in Warsaw reported back with good news. The Polish intelligence service, known as Agencja Wywiadu, had a training base with a villa that the CIA could use in Stare Kiejkuty, a three-hour drive north of Warsaw.

Polish officials asked whether the CIA could make some improvements to the facility. The CIA obliged, paying nearly $300,000 to outfit it with security cameras.

The accommodations were not spacious. The two-story villa could hold up to a handful of detainees. A large shed behind the house also was converted into a cell.

“It was pretty spartan,” the agency official recalled.

There was also a room where detainees, if they cooperated, could ride a stationary bike or use a treadmill.

On Dec. 5, 2002, Nashiri and Abu Zubaida were flown to Poland and taken to the site, which was code-named “Quartz.”

Five days later, an e-mail went out to agency employees that the interrogation program was up and running, and under the supervision of the Special Missions Department of the Counterterrorism Center (CTC).

Officials then began shutting down the prison in Thailand, eliminating all traces of the CIA presence.

Harsh interrogations

Agency executives tapped Mike Sealy, a senior intelligence officer, to run the Polish black site, according to former CIA officials. He was called a “program manager” and was briefed on an escalating series of “enhanced interrogation techniques” that were formulated at the CIA and approved by Justice Department lawyers. These included slapping, sleep deprivation and waterboarding, a technique that involved pouring water over the shrouded face of the detainee and creating the sensation of drowning.

“I do believe that it is torture,” President Obama said of waterboarding in 2009.

In Poland, Sealy oversaw about half a dozen or so special protective officers whom the CIA had sent to provide security. The number of analysts and officers varied. Polish officials could visit a common area where lunch was served, but they didn’t have access to the detainees.

There would soon be problems in the implementation of the interrogation protocols.

Agency officers clashed over the importance of Nashiri’s alleged role in the bombing of the USS Cole in Yemen in 2000; the attack killed 17 U.S. sailors.

“He was an idiot,” said the former CIA official, who supported the program. “He couldn’t read or comprehend a comic book.”

Other CTC officials thought Nashiri was a key al-Qaeda figure and was withholding information. After a tense meeting in December 2002, top CIA officials decided that they needed to get tougher with him, two former U.S. intelligence officials recounted.

A decision was made to dispatch a CIA linguist who had once worked for the FBI in New York. Albert El Gamil was of Egyptian descent and spoke Arabic fluently, but he was not a trained interrogator.

Gamil flew to Poland, where he subjected Nashiri to a mock execution and put a drill to the head of the blindfolded man, according to several former CIA officials. The CIA inspector general also reported on those events.

Top CIA officials learned about the incidents in January 2003 after a security guard at the facility sounded the alarm. Sealy and Gamil were pulled out of Poland and dismissed from the program, according to several former agency officials. They left the CIA a little later.

Both Sealy and Gamil declined to comment.

‘Dramatic positive results’

In March 2003, Khalid Sheik Mohammed was captured in the Pakistani city of Rawalpindi and brought to Poland. He proved difficult to break, even when water­boarded, according to several former CIA officials. Mohammed would count off the seconds, between 20 and 40, knowing that the simulated drowning always ended within a certain period.

An agency official said that one time, Mohammed fell asleep on the waterboard between sessions. But agency officials have said that he finally crumbled after extended sleep deprivation.

CIA officials assert that while in Poland, Mohammed, who has a sizable ego, began talking. He liked to lecture the CIA officers, who would then steer the conversations in ways that benefited them. He also liked to joust with his inquisitors. Once a female officer, who was later killed in Afghanistan, questioned Mohammed in Poland. She told him that she knew everything about him and that he shouldn’t lie to her, two CIA former officials said.

Mohammed leaned back in his chair and said, “Then why are you here?”

Abu Zubaida also provided important information to his interrogators, officials said. He identified people in photographs and gave what one official called “hundreds of data points.”

Officials said Abu Zubaida was even willing to help get new detainees to talk. “Allah knows I am only human and knows that I will be forgiven,” a former official recalled him saying.

Former agency officials directly involved in the program, such as the CIA’s former deputy director of operations, Jose Rodriguez, have said that the harsh techniques produced “dramatic positive results.”

The Senate Intelligence Committee intends to challenge such assertions when its report is made public. Sen. Dianne Feinstein (D-Calif.), the committee chairman, said her investigation “will provide a detailed, factual description of how interrogation techniques were used, the conditions under which detainees were held, and the intelligence that was — or wasn’t — gained from the program.”

Eventually, the CIA had to leave Poland, fearing that maintaining one location for too long risked exposure.

In September 2003, the Polish site was emptied. The CIA scattered detainees to Romania, Morocco and, later, Lithuania. Looking for a long-term solution, the CIA paid the Moroccans $20 million to build a prison it never used that was code-named “Bombay.”

In 2005, The Washington Post reported that the CIA had operated secret prisons in Eastern Europe. Human Rights Watch soon identified locations in Poland and Romania, and multiple European officials and news accounts have since confirmed the presence of these sites.

Before Porter J. Goss stepped down as CIA director in May 2006, the facilities in Romania and Lithuania were closed. Some of the detainees were sent to a Moroccan jail that had been previously used, and others were sent to a new CIA prison in Kabul called “Fernando,” which had replaced one known as “the Salt Pit.”

From those locations, 14 high-value detainees were shipped to the Guantanamo Bay military detention center in September 2006. Obama ended the interrogation program in 2009.

The previous year, Polish prosecutors opened a criminal investigation into what happened at the training base. They also quietly issued arrest warrants for CIA officials who had visited the black site.

It is not clear whether the warrants are still in effect.

Julie Tate contributed to this report.