Profile: Anas al-Liby
On the FBI's list of "most wanted terrorists", Anas al-Liby is accused by the US of being one of the masterminds behind the embassy bombings in Kenya and Tanzania in 1998, which killed 224 people.
In 2000, he was one of several indicted by a New York grand jury and has been on the run since then.
The charges against him include discussing with other al-Qaeda members a possible attack against the US embassy in the Kenyan capital, Nairobi, in retaliation for the American military intervention to restore peace in Somalia.
Mr Liby is also alleged to have carried out "visual and photographic surveillance" of the building in 1993 and "reviewed files" concerning possible attacks on Western interests in East Africa.
Malcolm W Vance, a former US intelligence officer, says Mr Liby is a very important al-Qaeda figure and could be one of the "top finds" the US intelligence has had since the death of al-Qaeda leader Osama Bin Laden.
"Operationally, he is more knowledgeable about the inner workings of al-Qaeda since he's been on board that organisation since the mid-1990s," he told the BBC.
"He was a computer programmer at one point, but became an operational combat commander for al-Qaeda. He was believed to be in Afghanistan and Pakistan along with the regular al-Qaeda leadership.
"It was very significant that he came back to Libya to what... appears was a very large broad-scale interlinking of all the al-Qaeda organisations in north Africa [he was going to organise]," Mr Vance adds.Civil war
Anas al-Liby was born in the Libyan capital, Tripoli, in 1964. His real name is Nazih Abdul-Hamed al-Ruqai.
The FBI lists several other aliases for him, including Anas al-Sabai and Nazih al-Raghie.
His involvement with al-Qaeda is thought to date from the early 1990s in Sudan. It is suggested he fled Sudan for Afghanistan when Bin Laden was forced to leave.
A Human Rights Watch document from 2007 also suggests he may have been detained by the CIA in 2002.
Mr Liby, an activist opposed to the rule of Libyan leader Muammar Gaddafi, was subsequently given political asylum in the UK - under unclear circumstances, the Guardian newspaper reports. He is believed to have lived in Manchester.
Some reports suggest he was arrested by British police in 1999 and terrorist training manuals were found in his flat. But he appears to have either fled the country or been released for lack of evidence.
The date of his return to Libya is unclear, possibly before or during the civil war in 2011 which led to the overthrow of Col Gaddafi.
A close friend, quoted by the Associated Press news agency, suggests Mr Liby's family returned a year before the civil war under a policy introduced by Gaddafi's son Saif al-Islam, to promote reconciliation with regime opponents who gave up violence.
With his capture and transfer from Libya, Anas al-Liby now appears destined for trial in the US where more light will be shed on his alleged role in one of al-Qaeda's deadliest attacks.