Judge James L. Pohl ruled Monday that Khalid Sheik Mohammed and four other alleged top al-Qaida terrorist operatives "can choose to voluntarily not attend a session," the Los Angeles Times reported.
Monday was the start of a weeklong pretrial hearing on 25 legal disputes. The five defendants face 87 charges, including conspiracy, murder, aircraft hijacking and terrorism. A trial is tentatively set for May.
Mohammed is the self-proclaimed mastermind of the 2001 attacks. The other defendants are Walid Muhammad Salih Mubarak bin Attash, Ramzi Binalshibh, Ali Abdul Aziz Ali and Mustafa Ahmed Adam al-Hawsawi.
The government asked the judge to force the defendants to attend the court hearings and the trial, and to bar them from staying in their jail cells in protest, the Times said.
Pohl, an Army colonel, said under statements of understanding, the defendants may decide on days of court hearings whether they want to remain in their cells and sign a document indicating their choice, the Times reported. They could watch the proceedings via video.
Chief prosecutor Brig. Gen. Mark Martins had argued that the defendants had no "right to refuse" to attend per military commission rules.
"The government should not be forced to proceed against empty chairs," Martins said.
Defense lawyers countered that their clients should be not forced to appear in court.
"There may be reasons why our clients don't want to come to court on a particular day," James Harrington, an attorney for Binalshibh, said. "Our clients may believe they don't want anything to do with this court, that they don't recognize the court."