In a quiet courtroom on the 21st floor, Osama bin Laden's son-in-law sits in a suit jacket and white shirt as a witness describes, in matter-of-fact tones, a plan to destroy airplanes with bombs hidden in shoes.
Sulaiman Abu Ghaith, who married a daughter of the al-Qaeda leader, is flanked by his lawyers. He listens as the witness discusses the details of the plot and prosecutors show a video he made in October, 2001, calling for a "storm of airplanes" aimed at American targets.
Mr. Abu Ghaith's trial, which began last week, is in many ways no different from the others under way at the federal courthouse in lower Manhattan: the bland legalese, the long-established protocol, the array of slightly rumpled New Yorkers serving as jurors.
But that is where the similarities end. Mr. Abu Ghaith is said to be the most senior al-Qaeda figure to stand trial in the United States. He is charged with conspiring to kill Americans and providing material support for terrorism. If convicted, he faces a possible sentence of life in prison.
His trial is an important moment in the long-running and often bitter debate in the United States about how and where detained members of al-Qaeda should face justice. The proceedings are a key test for those who believe the civilian courts are the best place to try such suspects.
In 2010, U.S. officials were forced to backtrack on a plan to bring Khalid Sheikh Mohammed, the alleged mastermind of the Sept. 11, 2001, 9/11 attacks, and other senior al-Qaeda leaders to face charges in New York. They are still awaiting trial in a military tribunal in Guantanamo Bay.
The current trial of an al-Qaeda figure in a civilian court "is showing that it can be done and it should be done," said David Kelley, a former top federal prosecutor in Manhattan who oversaw several terrorism-related prosecutions. Military tribunals have no track record on such cases, he said. "We should do what's tried and true."
Mr. Abu Ghaith's trial is notable for its normalcy. There is no visible additional security outside the courthouse, which sits just blocks from where the World Trade Center towers once stood. The only sign that something unusual is unfolding is an extra screening by metal detector just before entering the courtroom.
The trial is open to the press and the public at large. Earlier this week, the visitors included Ellen Judd, a professor at the University of Manitoba who lost her partner, Christine Egan, in the terrorist attacks of Sept.11, 2001. That morning, Ms. Egan, a nurse from Winnipeg, was visiting her brother, Michael, at his office in the South Tower.
Prof. Judd sat two rows behind Mr. Abu Ghaith with other family members of 9/11 victims. Seeing the process firsthand was "quite interesting," she said. For her, being present was part of "the mental exercise of thinking through how people can do such terrible things, and thinking about how to respond properly to it."
Mr. Abu Ghaith, 48, an imam from Kuwait, is not charged with involvement in the Sept. 11 attacks. U.S. authorities have described him as a confidant of Mr. bin Laden and a spokesman and propagandist for al-Qaeda – the group's public face in the months following the attacks on New York and the Pentagon.
Prosecutors showed clips from two videos made in October, 2001, and broadcast by the television channel Al Jazeera. In one, Mr. Abu Ghaith praises the men who carried out the 9/11 attacks. "They have done a good deed, they have transferred the battle into the heartland of America," he says. "The storm of airplanes will not abate, with God's permission."
Many more recruits are "yearning to death just as Americans yearn to live," he adds.
Mr. Abu Ghaith has pleaded not guilty. He told U.S. investigators after being apprehended in Jordan last year that Mr. bin Laden provided "bullet points" for the videos and that his role "was to deliver and build a speech" around those points. He also informed them that he was close to the al-Qaeda leader but not a member of the organization.
During the trial, jurors have heard from Saajid Badat, a British operative for al-Qaeda who was tasked with carrying out the shoe-bomb plot, but ultimately backed out. Mr. Badat said that in the fall of 2001, he engaged in "brainstorming" with Mr. Mohammed.
At one point, Mr. Mohammed took out a book of the world's tallest buildings and crossed out the pictures of the two World Trade Center towers, Mr. Badat said.
"I am ashamed to say that when he did this, he did it in order to make us laugh, as a joke," he testified, according to The New York Times.
One recent afternoon, two tourists from Alabama slipped into the back row of the courtroom. Mike Wishinsky, 52, said he and his wife had noticed television cameras outside the courthouse and decided to come inside. "I just wanted to see a little piece of history," Mr. Wishinsky said.
For Prof. Judd of Winnipeg, the apparent openness of the trial was heartening. "It is a good thing to hold people to account in as fair and legal a way as we can," she said, referring to the situation at Guantanamo Bay as "indefensible."
But even at a trial, the heart of the matter remains opaque. "It's the very controlled nature of the event," Prof. Judd said. "It's still not transparent why people do it."
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