A defense lawyer at Guantanamo Bay, Cuba, said Monday that there is “overwhelming circumstantial evidence” that the U.S. government is listening to privileged communications between high-value detainees accused of orchestrating the Sept. 11, 2001, attacks and their attorneys.

Cheryl Bormann, who represents Yemeni defendant Walid bin Attash, said devices designed to look like smoke detectors and placed in client meeting rooms were in fact audio monitors.

The issue of eavesdropping arose two weeks ago when the audio feed from the courtroom at Guantanamo Bay was mysteriously cut. To the apparent surprise of the military judge, Army Col. James Pohl, it was revealed that an unnamed government agency, listening for the potential release of classified information, controlled a “kill switch” to the feed provided to the public gallery and media centers.

The agency was not identified, but a prosector said it was the “original classification authority” — almost certainly the CIA in the case of matters concerning defendants in the 9/11 trial. The judge ruled that in the future only he could turn off video or audio from the proceedings.

The revelation about the audio feed switch led defense attorneys to question what else might be overheard and by whom, both in the courtroom and in the locations where they meet with clients.

In a statement Sunday night, the chief military prosecutor, Brig. Gen. Mark Martins, said that “no entity of the United States government is listening to, monitoring or recording communications between the five accused and their counsel at any location.”

James Connell III, an attorney for Ali Abdul Aziz Ali, told the court Monday that there are two audio feeds from the courtroom: The first to the public is “gated” and filters out general noise. The second, heard by the court reporter and the “original classification authority,” is “ungated” and picks up all sounds in the courtroom.

That raises the possibility that private conversations between the lawyers and their clients could be monitored. The judge said he would allow the defense to listen to three “ungated” recordings to get a sense of what extraneous sounds might be picked up.

The government, without acknowledging that anyone was listening to privileged communications, said it would switch the audio system in the courtroom so that speakers would be required to push a button to activate their microphones; currently, all audio is picked up unless the speaker presses a mute button.

A number of military and technical personnel are expected to testify about the issue Tuesday during pretrial hearings in the case against Khalid Sheik Mohammed, the self-proclaimed mastermind of the Sept. 11 attacks, and his four co-defendants.

One of Mohammed’s attorneys, David Nevin, said Monday that defense lawyers meet their clients in a place that is “owned by intelligence operatives.”

The five defendants were held at secret CIA prisons overseas before being transferred to Guantanamo Bay in September 2006. The government, however, has never clarified what role, if any, the CIA continues to have in their detention. Along with other high-value detainees, they are held at Camp 7, a high-security facility whose location at Guantanamo Bay is classified.

All other detention camps at Guantanamo Bay are run by the military, but there is no public information about the guard force at Camp 7 or whether CIA personnel have any role there.

Attorneys for the detainees do not meet them at Camp 7; they are transported to another facility for attorney-client meetings.