GUANTÁNAMO BAY, Cuba — The five men accused of masterminding the 9/11 attacks appeared in the military courtroom here at Guantánamo Bay on Monday, as their lawyers argued another round of pretrial motions in the government’s case.

The so-called “9/11 five” face five criminal charges, including conspiracy to commit the 9/11 attacks, attacking civilians, and murder in violation of the laws of war. But more than 16 years after the attacks, there is still no trial date set. The men have been arraigned here at Guantánamo Bay twice — once in 2008, under the Bush administration, and again in 2012, after the Obama administration reversed its effort to move the trial into civilian court.

The five men were brought into court by military police Monday, several minutes apart. Khalid Sheikh Mohammed, the alleged mastermind of the 9/11 attacks and perhaps the best-known of the defendants, was brought in second. He wore a skullcap, his beard cropped and dyed red. He and two other defendants, Ramzi bin al Shibh and Walid bin Attash, wore camouflage-pattern jackets.

The men are represented by separate legal teams, each led by civilian lawyers with experience trying death penalty cases. The trial judge, Army Col James Pohl, is expected to hear more than 20 motions this week—nearly all of them filed by the defense teams.

There are two days of open hearings scheduled: Monday and Thursday. Hearings on other days will be closed to the public.

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Among the most consequential questions the court will consider is whether the government can stop the defense from speaking with foreign nationals in countries where CIA black sites may have been located — and from speaking with Americans who may have knowledge of so-called enhanced interrogation techniques used at these sites. The government has invoked a national security privilege, declaring such information classified and off-limits.

On Monday morning, defense lawyers said that the restrictions have kept them from conducting investigations into the facts of the government’s case -- introducing a conflict between what the government has asked, and their obligations as lawyers.

“If we fail in our duties as lawyers, we’d be failing our client and we’d be failing the commission,” said David Nevin, the lead counsel for Khalid Sheikh Mohammed, the alleged mastermind of the 9/11 attacks.

Lawyers for Ammar al Baluchi, who is accused of financing the 9/11 hijackers, have said the restrictions will stop them from introducing exculpatory information about their defendant.

During a briefing for media on Sunday, Baluchi’s lead attorney, Jay Connell, said that on five occasions this year he has told members of the team to hold off on pursuing leads, and he will likely cancel an upcoming trip of his own related to the investigation.

“This investigation prohibition is killing us,” Connell said Sunday.

The commission Judge, Army Col. James Pohl, said Monday that he would not rule on these restrictions until he’s heard more discussion later this week.

But Pohl opened the door a little further on another defense motion, telling the court that he would compel a written declaration from Secretary of Defense James Mattis on the firing of the so-called convening authority, the civilian lawyer who oversees the military commission.

Harvey Rishikof, a former FBI lawyer, was appointed by Mattis in April but was fired along with his deputy earlier this month. There was no public explanation for the move, and lawyers for Baluchi have said the firings represent undue political influence by the Trump administration.

On Monday Pohl said he would ask for declarations from Mattis and Gary Castle, the acting Pentagon General Counsel, detailing the firings. The declarations, the judge said, would be due by March 19.

“We simply need to know why they were terminated,” the judge said of Rishikof and Brown.

Rishikof was replaced by an acting convening authority — a retired Army lawyer named Jim Coyne. In court Monday, Pohl opened the proceedings with a disclosure that he and Coyne served alongside each other in the Army’s JAG Corps prior to Coyne’s retirement.

Media and other observers are able to view the proceedings from a gallery room separated from the court by three sheets of glass. Five family members of 9/11 victims are also invited to watch from the gallery, where they are separated from other members of the public by a blue curtain.

The family members sat placidly Monday, but several chuckled late in the morning when a defense attorney asked for a second chance to make a point during discussion of a motion.

“Briefly,” the judge replied.