Prosecutors trying five men accused of plotting the September 11, 2001 attacks asked Wednesday that the defendants be excluded from their trial when classified evidence is heard.
Lawyers for the five, who include self-declared 9/11 kingpin Khalid Sheikh Mohammed, strongly opposed the move on the third day of a preliminary hearing held at Guantanamo Bay and broadcast to Fort Meade near Washington.
Mohammed, known as KSM, appeared before the hearing at the US prison in Cuba wearing a camouflage jacket and sporting a thick red beard. His four co-conspirators all dressed in traditional Afghan robes and caps.
Military prosecutor Joanna Baltes asked the judge to bar the accused from attending any sessions when classified information surrounding the case is addressed.
The five men were held incommunicado in secret CIA prisons from 2002 to 2006, before they were transferred to Guantanamo.
The detainees' treatment has come under close scrutiny. Mohammed is known to have been subjected to 183 sessions of waterboarding, the technique of simulated drowning which has been decried as torture by rights groups.
Mohammed's lawyer David Nevin argued that excluding his client, who faces the death penalty if convicted, should not be allowed.
"This is a capital case, we object to him being excluded from these proceedings at any time," Nevin said.
"By virtue of charging them with capital case, by seeking the court's authority to kill them at the end of the proceedings, they become authorized to attend all relevant evidence to their case," Nevin added.
Nevin said the classified portions of the case related to Mohammed's treatment since his incarceration.
"What we're talking about is the torture. Mr Mohammed has the right to be present when we are dealing with matters that address to his torture. We're talking about a capital case, we're talking about executing him," he said.
Judge James Pohl asked prosecutors whether it would be possible to split the prosecution up, or to exclude other defendants when classified information about another defendant was being heard.
But Baltes said splitting up the case would be complicated.
Other lawyers for the men also protested against moves to exclude their clients from parts of the hearings.
The five accused had a right to be present, Cheryl Bormann argued.
"It's the foundation of fairness... they have the right to be present, that's what statutes say," she said.
The hearing, due to be completed on Friday, aims to fix a trial date for the five men, who face the death penalty if convicted of plotting the attacks on New York and Washington which left nearly 3,000 people dead.