Military prosecutors say they have tapes of telephone calls between the alleged mastermind of the September 11 attacks, Khalid Sheikh Mohammed, and three of his accused co-conspirators talking in code about the plot months before it took place, a defence lawyer disclosed on Monday.

The lawyer, Jay Connell, revealed the existence of the tapes as part of a protest over plans to use them as evidence at the death-penalty trial of the alleged conspirators. More than 17 1/2 years after the attacks — in which 19 hijackers commandeered four commercial airplanes and crashed them into the World Trade Center, the Pentagon and a Pennsylvania field, killing nearly 3,000 people — there is still no date set for the trial in the proceedings at Guantánamo Bay.

Prosecutors gave defence lawyers the original audio and transcripts of their translation on September 30, 2016, Connell said, and made clear they planned to use them at trial. Defence lawyers sought to investigate their origins and later discovered that the original trial judge, Army Col James L. Pohl, had issued a secret order preventing them from knowing about the phone call collection system or asking questions about it.

Connell, who is representing Mohammed’s nephew, Ammar al-Baluchi, said prosecutors secretly obtained a ruling in August 2018 from Pohl forbidding defence lawyers from learning how the phone calls were collected or investigating that question. The phone calls in at least two languages were made between April and October 2001.

Connell said the restriction on investigating the origins of the tapes violated a defendant’s basic right to challenge the evidence being used against him. He argued in court on Monday that the evidence should be suppressed or that the case should be dismissed. He said the constraints the defense faces regarding the tapes violate the Sixth Amendment, which sets out the rights of defendants in a trial.

The military trial judges have yet to decide, however, which aspects of the Constitution apply at the military commissions, the war court established by President George W. Bush after the terrorist attacks.

A prosecutor, Clayton Trivett, responded that defence lawyers would be allowed to question an FBI linguist who compared samples of the voices of the defendants to the voices on the tapes to confirm they were Mohammed, al-Baluchi and two other alleged plotters.

Trivett said defence lawyers would be allowed to question an FBI analyst who decoded the conversation. The only restriction, he said, is on defense lawyers trying to investigate “how the United States government got those calls”, something prosecutors convinced the judge would endanger national security.

Pohl had said prosecutors could describe the evidence as having been acquired from “telephone calls from between April and October 2001 that were later determined to pertain to the planned attacks on September 11, 2001”.

Terry McDermott, co-author of The Hunt for KSM, said his research found that US satellites “randomly scooped up” calls between Mohammed and an alleged deputy, Ramzi Binalshibh. “The NSA intercepted calls but didn’t listen to them or translate them until after 9/11,” he said. “Afterward, they went through this stuff and found out what it was.”

Trivett did not disclose how or when the FBI got voice samples of the accused plotters. Connell questioned in court whether they were recorded during the years Mohammed and the other the defendants were held in the CIA’s secret prison system.

Trivett announced that the samples were not from the CIA black sites where the five alleged plotters were held before they were brought to Guantánamo for trial in 2006.

This week a new military judge, Col Keith Parrella of the Marines, is hearing lawyers and prosecutors argue in the 34th round of pretrial hearings since the five men were arraigned in 2012.

c.2019 New York Times News Service