Mr. Kotey declined to comment, instead referring to a lengthy letter he had filed with the court. The letter describes at times feeling sympathy for his captives, but such sentiments, he wrote, were “often brief and momentary.” He called himself a soldier carrying out orders and using harsh tactics that were necessary to fight the United States as part of asymmetrical warfare.
While Mr. Kotey said in the letter that he took responsibility for his actions and that his own capture and detention had led to reflection, he did not apologize for his crimes, writing that he was “slightly reluctant to use such terms like remorse.”
As part of his plea deal, Mr. Kotey agreed to meet with the families of the dead hostages and share information with F.B.I. agents and prosecutors, a process that has already started. If he fulfills his cooperation requirements, Mr. Kotey could be sent to Britain after 15 years to complete the remainder of his life sentence.
Earlier this month, a jury swiftly convicted El Shafee Elsheikh, 33, another Islamic State militant believed to be a member of the Beatles, on four counts of hostage-taking and four counts of conspiracy related to the deaths of the Americans.
At Mr. Elsheikh’s trial, Raj Parekh, the first assistant U.S. attorney, said Mr. Kotey and Mr. Elsheikh were terrorists and brothers in arms who reveled in sadism and were deeply tied to the kidnapping scheme.
“The evidence demonstrates that they grew up together, radicalized together, fought as high-ranking ISIS fighters together, held hostages together, tortured and terrorized hostages together,” Mr. Parekh said. “And after Emwazi was killed, Elsheikh and Kotey were ultimately captured in Syria together.”
Prosecutors recounted how the hostages had been beaten and waterboarded and endured mock executions. One Danish hostage was hit 25 times in his ribs on his 25th birthday, Mr. Parekh said. Some were freed after ransoms were paid.