The five suspected plotters of the September 11 attacks were back in court on Monday with censorship at the centre of how their pre-trial hearings have been conducted at Guantanamo Bay.
A military judge overseeing the hearings ruled last month that the US government censored a discussion involving secret CIA prisons, preventing it from being heard outside the courtroom, and ordered such censorship to stop.
Monday's hearing began with David Nevin, the lawyer of alleged 9/11 mastermind Khalid Sheikh Mohamed, being granted a 24-hour delay so that he could interview two officials involved in monitoring communications at Guantanamo.
Nevin said he had good grounds to believe his discussions with Mohamed, both in the courtroom and outside it during prison visits, had been monitored.
"This is a genuine concern - we have to go to the bottom of this before we can carry on our proceedings," Nevin said in legal argument.
"The confidentiality of our communications is at issue. If someone has the ability to kill the switch... it raises the spectre that they have the ability to listen to our communications," he added.
The five men suspected of plotting the attacks against the Twin Towers and the Pentagon, and involving another airliner which crashed in Pennsylvania - killing nearly 3,000 people in total - face the death penalty if convicted.
The hearings at the US naval base in Guantanamo on the southeastern tip of Cuba are carried on closed circuit television with a 40-second delay to journalists, relatives of victims and human rights activists observing the proceedings from outside the courtroom.
The delay enables a security officer, seated next to the judge, to block the feed when the exchanges touch on matters that are considered classified.
Cheryl Bormann, an attorney for Yemeni suspect Walid bin Attash, said the censorship issue cut to the heart of the case.
"It's a huge problem," Bormann said, noting the "logistical nightmare that Guantanamo Bay presents," and that she had evidence that "a listening device... with the ability to record" had been placed in a "smoke detector."
Seeking to allay concerns from the defence counsel, the chief prosecutor General Mark Martins proposed that a microphone be used that has a "push to talk switch," to prevent anyone listening in.
A "push to mute switch" is currently used on the court microphones.