(CNN) -- U.S. authorities regard Sulaiman Abu Ghaith, 47, as a core member of al Qaeda -- present with the group's leadership during Osama bin Laden's final stand at Tora Bora in December 2001, and subsequently as one of its key spokesmen.
He is married to one of the late al Qaeda leader's daughters, Fatima.
After al Qaeda's leadership was scattered, Abu Ghaith escaped to Pakistan and subsequently turned up in Iran. The Islamic Republic was not overjoyed by his presence and in 2003 tried to return him to his country of birth: Kuwait. But the then-Kuwaiti foreign minister said the idea had been rejected. Abu Ghaith had been stripped of his Kuwaiti citizenship soon after 9/11.
And so Abu Ghaith spent much of the next decade in Iran, in some sort of loose house arrest. According to Turkish media reports he arrived in Ankara at the beginning of February -- traveling on a forged Saudi passport.
Sources in Turkey say he checked into an upscale hotel in the capital, but was subsequently detained at the United States' request.
The Turkish authorities were apparently anxious that to extradite him directly to the United States could provoke a backlash by al Qaeda sympathizers. He had not committed any crime on Turkish soil -- and according to Turkish law, foreign nationals who enter the country on a forged passport must be deported to the country from which they had traveled.
But the Iranians refused to take him back, according to Turkish sources. So after several weeks in limbo, the decision was made to deport Abu Ghaith to Kuwait. And a few days ago, according to one source, he was put on a plane for Amman, Jordan -- an intermediate stop on his journey home. But somewhere along the way, he was handed over to U.S. custody and diverted to New York.
The capture was confirmed Thursday by two administration officials and a federal law enforcement official.
It's unclear how much, if anything, Abu Ghaith knew about the planning for the 9/11 attacks.
One detainee at the naval base in Guantanamo Bay, Adel Zamel Abd al Mahsen al Zamel, is said to have moved his own family and Abu Ghaith's from Kuwait to Afghanistan "immediately prior to the September 11 2001 attacks," according to his detainee assessment.
According to the 9/11 Commission report, there was disagreement among al Qaeda's leadership about launching a major operation against the United States in 2001. Taliban leader Mullah Omar was opposed, but those who reportedly sided with bin Laden included Khalid Sheikh Mohammed -- and Abu Ghaith.
The picture that emerges of Abu Ghaith from the testimony of detainees at Guantanamo Bay is of someone close to decision-making in al Qaeda immediately after the 9/11 attacks. Several reported seeing him in meetings at Tora Bora with other al Qaeda leaders.
Other detainees describe meeting him in Kabul, Kandahar (a Taliban stronghold) and at al Qaeda's al-Faruq training camp. Said Salih Said Nashir said Abu Ghaith addressed detainees there. And his phone number was found on the SIM card of another detainee.
A U.S. Justice Department complaint said, "On the morning of September 12, 2001, Abu (Ghaith) appeared with Bin Laden and Zawahiri, and spoke on behalf of al Qaeda, warning the United States and its allies that "[a] great army is gathering against you" and called upon "the nation of Islam" to do battle against "the Jews, the Christians and the Americans."
As the United States launched air strikes against Taliban and al Qaeda targets in October 2001, Abu Ghaith emerged as the voice of al Qaeda, recording one video message in which he said: "The Al-Qaeda organization declares that Bush Senior, Bush Junior, Clinton, Blair and Sharon are the arch-criminals from among the Zionists and Crusaders."
And in a later statement, published in 2002, he said: "We are continuing with our blows against the Americans and the Jews, and with attacking them, both people and installations [so as to stress] that what awaits the Americans will not, Allah willing, be less than what has already happened to them. America must prepare itself; it must go on maximum alert."
In the same statement he said: "The Americans have still not tasted from our hands what we have tasted from theirs ... We have (the) right to kill four million Americans," including with chemical and biological weapons.
One Moroccan detainee interviewed after being transferred home from Guantanamo said he and Abu Ghaith had spent time in bin Laden's company after the beginning of the U.S. bombing offensive in Afghanistan in October 2001 before traveling with al Qaeda's leader to Tora Bora.
"During the month of Ramadan....we entered Tora Bora where we stayed for 20 days. From there, Ayman al-Zawahiri fled accompanied by Suleiman Abu Ghaith and Uthman, the son of Osama Bin Laden," the detainee stated.
And in an interview with Al Majallah magazine in 2002, one of Osama bin Laden's wives described Abu Ghaith as one of the closest confidants to the al Qaeda leader.
In the 1990s, Abu Ghaith developed a reputation in Kuwait as a militant preacher
Nasir al Bahri -- who was bin Laden's personal bodyguard in the late 1990s -- told the newspaper al Quds al Arabi in 2005 that Abu Ghaith "gave a Friday sermon in Kuwait and spoke about Osama bin Laden and defended him and about the Al-Qa'ida Organization.... He attacked the United States and its allies, and incited the youths against the United States ... He was immediately arrested."
"I think that the harassment he faced in Kuwait and the ban on his sermons there made him go to Afghanistan and officially join the al Qaeda organization," al Bahri said.
It was the beginning of a long journey that will culminate in Abu Ghaith's appearance in a Manhattan federal courtroom Friday.