A New York jury on Wednesday found Osama bin Laden's son-in-law guilty of conspiracy to kill Americans and supporting terrorists as an impassioned Al-Qaeda spokesman in 2001-2002.
Suleiman Abu Ghaith, 48, now faces life in a maximum security American prison after a three-week trial, which has been the highest-profile Al-Qaeda case to reach a US federal court.
The preacher from Kuwait stood impassively as the court clerk read out the verdict, declaring him guilty of conspiracy to kill Americans, conspiracy to provide material support and providing material support to terrorists.
The convict is most famous for sitting next to bin Laden in a video on September 12, 2001 as the Al-Qaeda mastermind claimed the 9/11 attacks that killed nearly 3,000 people the day before.
Prosecutors said the first thing bin Laden did after the hijackings was recruit the talented, respected orator to take Al-Qaeda propaganda global as the Twin Towers lay smoldering.
In videos, Abu Ghaith threatened a "storm of airplanes," proof the government said that he was implicated in a December 2001 plot to blow up a transatlantic flight with a shoe bomb.
Terror cases in civilian courts
The 12-person jury took just four hours of deliberations to return the unanimous verdict. Afterwards, Abu Ghaith touched his heart in thanks, smiling at his lawyers.
Wearing his habitual dark suit, with open-necked white shirt, he appeared relaxed despite having pleaded innocent.
The government and campaigners seized on the trial as proof that terror cases could be tried more effectively in civilian courts as pressure builds to close the Guantanamo Bay prison camp.
"This outcome vindicates the government's approach to securing convictions against not only this particular defendant, but also other senior leaders of Al-Qaeda," said US Attorney General Eric Holder.
Defense to appeal
"We hope this verdict brings some small measure of comfort to the families of the victims of Al-Qaeda's murderous designs," said Manhattan US attorney Preet Bharara in a statement.
Defense lawyer Stanley Cohen told reporters that he would appeal, accusing the judge of being "coercive," and taking issue with Judge Lewis Kaplan's instructions to the jury and his decision not to allow presumed 9/11 plotter Khalid Sheikh Mohammed to testify.
He said his client was "stoic" and "at ease."
"He has confidence that this is not the end but the beginning. We think there are a number of compelling issues for an appeal," Cohen said.
US prosecutors alleged that the fiery orator was Al-Qaeda's main messenger after the 9/11 attacks.
Video clips, his confession to an FBI agent en route to the United States last year and his testimony on the stand all proved his guilt, they argued.
"In the most important period of time in Al-Qaeda's savage history Suleiman Abu Ghaith was Osama bin Laden's principal messenger," assistant US attorney John Cronan told the court.
"Al-Qaeda is about murdering Americans and regardless of role, participating in that conspiracy in any way whatsoever is a crime. Did that man knowingly participate in that conspiracy? Of course he did."
The defense said there was no evidence linking Abu Ghaith to any specific conspiracy, presenting him as a pious imam who "had no problem" with the Americans who liberated his country after the 1990 Iraqi invasion.
Kaplan told the jury that should Abu Ghaith be deemed a conspirator, under US law he would be responsible for any acts that happened before he joined.
Abu Ghaith fled Afghanistan for Iran in 2002. He was arrested in Turkey in 2013 and sent to Jordan, where he was transferred to US custody.