Osama Bin Laden's son-in-law Sulaiman Abu Ghaith, who was an al Qaeda spokesman after 9/11, has been convicted of terrorism-related charges at a trial in New York, according to BBC News.

He could face life in prison when he is sentenced in September for conspiracy to kill Americans and aiding al Qaeda.

The Kuwaiti clergyman was captured in Jordan last year and brought to the U.S. He is the highest-ranking al Qaeda figure to face trial on U.S. soil since the attacks.

The jury returned a guilty verdict on three charges: conspiracy to kill Americans, conspiring to provide support to al Qaeda, and providing support to al Qaeda. The verdict came after about five hours of deliberation.

Videos showing Abu Ghaith threatening America with no end to the "storm of airplanes'' were shown to jurors, but he argued his role was a purely religious one, aimed at encouraging all Muslims to rise up against their oppressors.

He testified that Bin Laden had asked him to be al-Qaeda's spokesman on the night of the 9/11 attacks.

On Monday, March 24, during closing arguments, Assistant U.S. Attorney John Cronan highlighted what he said was the importance of Abu Ghaith's post-9/11 status.

"Going to that man was the very first thing Osama Bin Laden did on September 11 after the terror attacks," he said. "The defendant committed himself to al Qaeda's conspiracy to kill Americans, and he worked to drive other people to that conspiracy."

Denying he was an al Qaeda recruiter, Abu Ghaith insisted he had agreed to meet with Bin Laden in a cave on the night of September 11 out of respect for Bin Laden's standing as a sheikh.

One witness at the trial was a British man who was supposed to join Richard Reid in the attempted shoe-bomb airline attack of December 2001. The man left the plot after his parents warned him against involvement in terrorism.

He did not know Abu Ghaith, but prosecutors introduced evidence to show Abu Ghaith knew of such detailed plans for more air attacks on the U.S., as he promised in his videos.

Abu Ghaith's defense lawyers argued there was "zero evidence" that the 48-year-old former teacher knew about any conspiracies and that the prosecution case was based purely on "ugly words and bad associations."

In a surprise move, the cleric took the witness stand in his own defense, denying he helped plot al Qaeda attacks and claiming he never became a formal member of the group.

Abu Ghaith, who is one of the highest-ranking al Qaeda linked figures to face a civilian jury on terrorism-related charges, is married to Bin Laden's eldest daughter Fatima.

Bin Laden, a founder of al Qaeda, was killed by U.S. forces in May 2011 at his hideout in Pakistan.

As in several other terrorism trials held in American civilian courts, the jury remained anonymous.