This article was produced in partnership with the Pulitzer Center on Crisis Reporting.
GUANTÁNAMO BAY, Cuba — The C.I.A. contractor who interrogated Khalid Shaikh Mohammed, the man accused of plotting the Sept. 11, 2001 terror attacks, testified on Monday that he threatened to kill one of Mr. Mohammed’s sons if there was another attack on America.
James E. Mitchell, a psychologist who helped develop the C.I.A.’s interrogation program, said he made the threat after he had waterboarded Mr. Mohammed for the 183rd time. He said he did so after he consulted a lawyer at the agency’s Counterterrorism Center about how to make the threat without violating “the Torture Convention.”
He said he was advised to make the threat conditional.
So, before telling Mr. Mohammed, “I will cut your son’s throat,” Dr. Mitchell said, he added a series of caveats. They included “if there was another catastrophic attack in the United States,” if Mr. Mohammed withheld “information that could have stopped it,” and “if another American child was killed.”
Dr. Mitchell was testifying in a pretrial hearing that has been focused in part on the torture of the defendants in the Sept. 11 case before they were sent to the military prison at Guantánamo Bay.
Dr. Mitchell said he made the threat in March 2003 as “an emotional flag” as he was transitioning from waterboarding and other violent “enhanced interrogation techniques” to more traditional questioning of Mr. Mohammed.
Pakistani security forces reportedly seized Mr. Mohammed’s sons, Abed, 7, and Yusuf, 9, in September 2002 in a joint raid with United States forces that seized Ramzi bin al-Shibh, another defendant in the 9/11 war crimes case. Mr. Mohammed would be captured in Pakistan six months later. He was at a C.I.A. black site in Poland later that month when Dr. Mitchell made the threat.
The boys were subsequently released and are believed to be living in Iran, with their mother, but Mr. Mohammed apparently did not know the fate of the boys until many years later, after the C.I.A. transferred him to the Pentagon-run prison complex at Guantánamo Bay.
It was one of the most emotional moments in five days of testimony by Dr. Mitchell on the question of torture before the trial of five men accused of conspiracy in the attacks is scheduled to start next year. He was unapologetic.
Dr. Mitchell said that eight children died in the 9/11 hijackings that killed 2,976 people in New York, Pennsylvania and at the Pentagon. Then he gestured toward Mr. Mohammed, who was sitting with his lawyers 25 feet away and declared, “He’s smirking.”
The smirk, or any emotion, was not visible from a spectator’s gallery at the back of the court. Mr. Mohammed appeared impassive throughout the testimony, occasionally fingering his long orange-dyed beard, while his lawyer, David Nevin, questioned Dr. Mitchell.
“Do you think that telling someone that might instill fear in that person?” Mr. Nevin asked.
“Yes I do,” Mr. Mitchell replied. “That was the only time that I made that threat to him.”
Dr. Mitchell said he invoked Mr. Mohammed’s children during interrogations again that same month, March 2003, in pressing for details on the whereabouts of Mr. Mohammed’s nephew, Ammar al-Baluchi. Mr. Mitchell quoted himself as saying it would be “safer” for Mr. Mohammed’s family to help the United States find Mr. al-Baluchi rather than “have him running around and the U.S. dropping a missile on him.”
Mr. al-Baluchi, who is charged in the same case with helping the 9/11 hijackers with money transfers and travel arrangements from the United Arab Emirates, where he worked at the time, was captured in Pakistan in April 2003 in a vehicle with another defendant in the case, Walid bin Attash.
Zeke Johnson, a program director for Amnesty International who was watching the proceedings, said the threat to kill one of Mr. Mohammed’s children no doubt broke the law.
“Threatening to kill a detainee’s child would violate the Convention Against Torture and be illegal,” Mr. Johnson said. “Anyone who broke the law must be held accountable — from those at the top who ordered it to those who carried it out.”