GUANTANAMO BAY, Cuba — Accused 9/11 mastermind Khalid Sheikh Mohammed and the man who waterboarded him at a secret CIA black site are to meet face-to-face in a Guantanamo Bay courtroom Tuesday.

Dr. James Mitchell, 67, will be questioned by Mohammed's defense team and those of four other alleged 9/11 plotters in what is expected to be at least a week of testimony in a secretive military proceeding at the U.S. naval base on the island of Cuba. The architect of the CIA’s post-9/11 enhanced interrogation program, labeled torture by critics, helped design and implement the program used against those considered high-value detainees and al Qaeda members.

Following the attacks that killed more than 3,000 Americans, Mohammed, 55, a lieutenant of al Qaeda founder Osama bin Laden, was captured in Pakistan in 2003 and faced interrogation at CIA sites in Afghanistan and Poland before being transferred to Guantanamo Bay in 2006, where he faced further questioning by the FBI. The CIA waterboarded Mohammed 183 times.

The case against the five men, set for trial early next year, has moved slowly. The pretrial hearings that started Tuesday are expected to span two weeks and are the 40th in the case. A judge must rule on whether confessions made to the bureau will be admissible.

It will be the first time a designer of the contentious program will provide on-the-record insights in the case. Mitchell, a psychologist and retired Air Force officer, told the Washington Examiner during a chance dinner encounter at Guantanamo Bay’s Gold Hill Galley on Monday that he had been instructed not to talk about about his impending testimony.

It's a very different scene from the pair's first meeting.

“‘Call me Mukhtar,’ KSM demanded in perfect, easily understood English and with a hint of pride in his voice,” Mitchell wrote in his 2016 book Enhanced Interrogation. “Then, in a lecturing tone, he added, ‘Mukhtar means ‘the Brain.’ I was the amir of the 9/11 attacks.’”

Lt. Col. Derek Poteet, one of Mohammed’s lawyers, said Sunday: “I’ve tried to think to myself, what would it be like if I had gone through what they went through and then to be again in the same room with the person who had done that to me, and it's difficult to imagine.”

James Connell, a civilian lawyer for Mohammed’s nephew, Ammar al Baluchi, told the Washington Examiner that part of his goal in grilling Mitchell would be to show “the deep involvement of the FBI” in the CIA’s interrogation program.

“This is probably one of the most consequential hearings we have had yet,” said Alka Pradhan, another Baluchi attorney.

Mitchell, sporting a white beard for the hearing, has always defended the methods used against the alleged 9/11 mastermind. “I concluded that conducting coercive interrogations on a small number of Islamic terrorists who were actively withholding information that could disrupt a potentially catastrophic attack was justified as long as those methods were lawful, authorized, and carefully monitored,” he wrote in his book. "In the turmoil and confusion after the attacks of 9/11 and under the threat of new ones, possibly involving a nuclear device, the CIA followed the president’s orders and took forward-leaning action that kept Americans safe."

Mitchell joined the Air Force in 1975, where he learned to disarm explosives in the Alaskan wilderness as a bomb technician and spent years as a hostage negotiator in Texas. He received his master’s in psychology at the University of Alaska in the early 1980s and a Ph.D. in psychology from the University of Southern Florida in 1986, where his thesis centered on the effect of diet and exercise on hypertension.

He became a clinical psychologist at the Air Force Survival School, where he taught military members how to resist harsh interrogations. The interrogation techniques developed by Mitchell and Dr. Bruce Jessen, who is also expected to testify, included sleep deprivation, isolation, cramped confinement, face slapping, stress positions, shoving detainees against flexible walls, and waterboarding. He has said waterboarding does not do permanent harm.

“It sucks, you know,” he said. “I don’t know that it’s painful. I’m using the word distressing.”

Mitchell, Jessen, and Associates, founded in 2005, eventually received $81 million out of an authorized $180 million from the government prior to the contract's termination in 2009, although much likely went to paying company employees, some of whom were probably former CIA interrogators. Mitchell revealed in a 2017 deposition that he received $1,800 per day for overseas work and $15,000 for travel for his first CIA trip in 2002, centered on Abu Zubaydah, a suspected al Qaeda terrorist whom Mitchell eventually waterboarded.

Mitchell, who also waterboarded alleged USS Cole bombing mastermind Abd al Rahim al Nashiri, claimed in his book that CIA leadership later continued pushing him to expand the enhanced interrogations, even as he grew hesitant.

“You guys have lost your spine" and "you guys are pussies," Mitchell recounted CIA leaders saying. “There was going to be another attack in America, and the blood of dead civilians are going to be on your hands.”

Debate over the CIA program lasted for years, with the Democrat-led Senate Intelligence Committee concluding in 2014 that it “was not an effective means of acquiring intelligence or gaining cooperation from detainees” and that the interrogations “were brutal and far worse than the CIA represented to policymakers and others.” Of the 119 suspected terrorists held in CIA custody at some point, 39 detainees were known to have been subjected to those techniques.

But Republicans, as well as former CIA Directors George Tenet, Porter Goss, and Michael Hayden, pushed back.

"We have no doubt that the CIA's detention program saved lives and played a vital role in weakening al-Qaeda while the program was in operation," Republican committee members wrote, saying the report's conclusions were biased.

The CIA, then led by John Brennan, acknowledged “shortcomings” and “mistakes” but insisted the program “helped thwart attack plans, capture terrorists, and save lives.” The agency would later say that “intelligence acquired from these interrogations has been a key reason why al-Qaeda has failed to launch a spectacular attack in the West since September 11, 2001.”

President Barack Obama banned the use of the techniques with a 2009 executive order, and a 2015 law limited interrogation methods.