Defense lawyers want Pohl to throw the case out because of “unlawful command influence,” a military expression for inappropriate meddling by a senior officer. MacDonald becomes the most senior U.S. government official ordered to testify at Guantánamo. Martins, the chief prosecutor, said MacDonald would testify in person at the court rather than by video-teleconference.

The drama of the day occurred out of earshot of the five men accused of conspiring in the Sept. 11 hijackings that killed nearly 3,000 people in New York, Pennsylvania and at the Pentagon. Mohammed and the others declined to attend the hearing, a pre-trial prerogative the judge has granted them, and also declined an offer to listen to him remotely.

Monday’s outside censorship episode occurred on the first day of proceedings after the judge formally approved the 40-second audio delay in the Sept. 11 trial, rejecting an American Civil Liberties Union argument that it transformed a live court into a “censorship chamber.”

The way the Guantánamo war court works is, spectators watch the proceedings live inside a soundproof room at the back of the court, hearing the audio 40 seconds later. If the court security officer functioning as a censor deems what is being said is a national security secret, he pushes a button and obscures the sound with white noise.

A red emergency light then spins in court to signal to everyone inside the tribunal chamber that the outside world can no longer hear them.

White noise has silenced the court three times since Mohammed and his fellow defendants were arraigned on May 5, and in each instance the judge or prosecutor concluded it was not legitimately censored, or “closure” as the lawyers and judge refer to it. All three instances occurred while defense lawyers were speaking — two of them U.S. military officers arguing to the judge in uniform.