US prosecutors on Monday asked a New York judge to prevent America's most high-profile terror detainee from testifying to defend Osama bin Laden's son-in-law.
The government made the request to Judge Lewis Kaplan in a memorandum filed to the federal court in New York's southern district.
The defense argues that testimony from Khalid Sheikh Mohammed, the self-styled 9/11 mastermind held at Guantanamo Bay, "could raise reasonable doubt as to the charges before the jury."
Mohammed says Suleiman Abu Ghaith never played a military role in Al-Qaeda and had nothing to do with a December 2001 plot to bomb a transatlantic US passenger jet.
Kaplan must now decide whether to admit his testimony.
Abu Ghaith is on trial accused of conspiracy to kill Americans, conspiracy to provide support to terrorists and providing support to terrorists.
The 48-year-old from Kuwait denies the charges. He faces life imprisonment if convicted by the jury at a trial just streets away from where the 9/11 attacks brought down the Twin Towers.
Mohammed's 14-page testimony, in response to questions sent to him through his lawyer, has been vetted by US intelligence agents and submitted to Abu Ghaith's lawyers.
Government prosecutors wrapped up their case on Friday and the defense called its first witnesses on Monday.
The defense argues that, while Abu Ghaith made incendiary remarks, he did not conspire to kill Americans and was not involved in a December 2001 shoe bomb plot as alleged.
"The defendant did not play any military role and did not receive any military training at any time," said a summary of Mohammed's testimony submitted to court by the defense.
"The detainee never communicated to the defendant anything about the shoe bomb plot and would not have done so; nor did he ever see him in the company of (shoe bomber) Richard Reid," it added.
Abu Ghaith is most famous for appearing in a video with bin Laden the day after the 9/11 attacks. The prosecution says he was hired to recruit young men all over the world for Al-Qaeda.
"Media activities and military operations were compartmentalized in such a way that individuals involved in media would not have prior knowledge of coming operations," according to Mohammed.
Abu Ghaith is the most high-profile alleged Al-Qaeda member to face trial in a US federal court rather than at Guantanamo Bay, which the White House has promised to close.
Married to bin Laden's daughter Fatima, US prosecutors say Abu Ghaith worked for Al-Qaeda until 2002, when he fled Afghanistan after the US invasion for Iran. He was captured in 2013.