One of the architects of the CIA's torture program for the accused Sept. 11 terrorists testified Wednesday in a Guantánamo Bay courtroom that he eventually came to believe that those torture techniques had gone too far and verged on breaking the law.

Testifying publicly under oath for the first time as part of a pretrial hearing for the criminal case against five accused Sept. 11 terrorists, psychologist and interrogator James Mitchell spoke specifically and graphically about one prisoner, Abu Zubaydah, who was waterboarded more than 80 times at a CIA site overseas. He has been held at Guantánamo for more than 13 years and has never been charged with a crime.

According to Mitchell's testimony, he thought they'd gotten all the information they could from Zubaydah, who had agreed to cooperate. Mitchell wanted the waterboarding to stop and helped draft a message to CIA headquarters saying that "the intensity of the pressure applied to him thus far approaches the legal limit" and that Zubaydah's mental state was deteriorating dangerously.

He said the CIA told them to keep going because Zubaydah might still be withholding valuable information about an imminent U.S. attack. In Mitchell's words, "They were absolutely convinced he had something cooking." Mitchell says he agreed to waterboard Zubaydah just one more time, but he wanted a senior CIA official to come see in person what it looked like. A senior CIA official did attend that waterboarding, during which — Mitchell testified — Zubaydah was having involuntary body spasms and was crying. Mitchell said he and others in the room became tearful.

"I thought it was unnecessary, and I felt sorry for him," Mitchell testified.

Mitchell, who personally waterboarded alleged Sept. 11 mastermind Khalid Sheikh Mohammed, began testifying on Tuesday and is expected to continue through the week.

The CIA paid a company owned by Mitchell and his partner, Bruce Jessen, another psychologist, more than $80 million to develop the torture program ultimately used by the CIA on suspected terrorists: waterboarding, stress positions and mock burials, among others. Mitchell and Jessen took a training program meant to teach the U.S. military to resist torture and reverse-engineered it. Once the public learned about the practices, the CIA canceled Mitchell and Jessen's contract amid international controversy in 2009. Jessen is expected to testify after Mitchell.

Mitchell and Jessen say those methods were meant to be more uncomfortable than painful, but they acknowledge that some interrogations got out of control and say it's not their fault that other interrogators used the techniques in abusive and unauthorized ways. Mitchell says he got to the point where he didn't want to be involved anymore but says officials above him told him he'd lost his spine and it would be his fault if more people in the U.S. died in a catastrophic attack.

"The implication was that if we weren't willing to carry their water, they would send someone else who would do it, and they may be harsher than we were," Mitchell testified.

Mitchell says he came to Guantánamo Bay for the Sept. 11 victims and their families, emphasizing the climate of fear after the 2001 terrorist attacks. He testified that the CIA had been afraid that another attack was imminent, possibly one with the use of nuclear or biological weapons. He says the government was going to do whatever was necessary to prevent that, saying that the CIA was "going to walk right up to the line of what was legal, put their toes on it and lean forward."

Mitchell's revelations suggest that the CIA was willing to lean forward further than Mitchell himself. The CIA declined to comment on the testimony. Still, Mitchell spoke defiantly and unapologetically. He insisted that he was protecting his country and would do so again if given the chance, despite his own testimony indicating that he tried to draw a line in the sand and despite internal debate within the CIA over whether they were venturing into illegal territory.

"I thought my moral obligation to protect American lives outweighed the temporary discomfort of terrorists who had voluntarily taken up war against us," he testified.

Mitchell has been called as a witness in the Sept. 11 case because defense attorneys want to use him to support their argument that the evidence gathered from the defendants by the FBI should not be presented at trial because it has been tainted by torture. The FBI did not use torture to gather its statements, but those statements were gathered after the CIA's use of torture. The defense attorneys have argued that once a person has been tortured, you cannot trust anything they tell any interrogator. The statements given by those defendants to the CIA are already inadmissible, because they were not given voluntarily. Mitchell says the CIA was never interested in prosecuting the prisoners.

The pretrial hearings for the Sept. 11 trial, which is scheduled to begin next January, have been going on for years. As NPR previously reported, one major reason for the slow pace has been the use of torture that happened at the CIA's overseas sites. In a 2008 statement, former CIA Director Mike Hayden said that waterboarding in particular had not been used since 2003.

"The Agency's decision to employ waterboarding in the wake of 9/11 was not only lawful, it reflected the circumstances of the time," the statement read. "Those two realities have changed."