Mystery solved, if there was any doubt: It was the CIA that hit the mute button in the war court earlier this year when a defense lawyer for the accused 9/11 mastermind began talking about the CIA’s secret overseas prisons, the lawyer said Monday.

The Jan. 28 episode so embarrassed Army Col. James Pohl, the judge in the Sept. 11 terror case, that he ordered the kill switch unplugged, an order the agency apparently honored because no outside entity has censored the court since.

Prosecutors had only allowed the kill-switch operator to be identified by the codename “OCA,” short for Original Classification Authority.

But Monday, attorney David Nevin, representing Khalid Sheik Mohammed, whom the CIA waterboarded 183 times, unmasked the OCA in open court while describing to the judge the slow pace of discovery in a Defense Department investigation of whether anyone else has the power to listen in on the war court, specifically their confidential attorney-client conversations.

“We recently learned that was the CIA, that CIA was controlling that location of the feed,” Nevin told the judge.

And this time nobody muted him for uttering the initials of the Central Intelligence Agency

The strange censorship episode occurred in January just as Nevin was asking the judge to issue a protective order on whatever remnants exist of the CIA’s secret overseas prison network. Pohl’s the judge who similarly declared the Abu Ghraib prison in Iraq a crime scene in 2004.

Pentagon officials at the time refused to confirm that the CIA controlled the audio from the court to the spectator’s gallery and several closed-circuit TV sites. Since unplugged, only the judge and a security officer at his elbow can silence the court — by hitting a button that triggers white noise and a red spinning light.

Instead, the prosecutor in charge of classified information, Joanna Baltes of the Justice Department, provided the court a carefully crafted written statement that called the hidden-hand controlling the court audio system “the OCA,” an acronym for Original Classification Authority.

Mohammed and his four co-defendants were held in secret overseas prisons until 2006, when President George W. Bush ordered them brought here for a variation on this death-penalty terror tribunal alleging they orchestrated the Sept. 11, 2001 attacks that killed 2,976 people. The Guantánamo war court functions like no other, with spectators listening behind soundproofed glass or on a secured video feed with a 40-second audio delay to make sure the public never hears about the alleged terrorists’ capture or CIA interrogations in a secret prison network President Barack Obama shut down on taking office.

Still unclear was whether the hidden-hand censor was reaching into the court to silence it from somewhere on this U.S. Navy base in southeast Cuba, headquarters in Langley, Va., or elsewhere.

Nevin made the disclosure in a day of mostly dry arguments in the Sept. 11 case that sought to have the case itself dismissed on a series of legal grounds, including one that said Congress created an illegal court at Guantánamo by limiting it only to foreign nationals.