Several people in Spain have been arrested, accused of having a direct link to Mohammed Atta, the apparent ringleader of the 11 September attacks. Investigators say they may have provided logistical support to the suicide hijackers.
The men are also accused of acting as recruitment officers for al-Qaeda, arranging for young men to be provided with false documentation and sent to Afghanistan for training.
The cell began to take shape in 1994, according to investigative Judge Baltazar Garzon, who has issued a detailed but sealed indictment. The group was led by Anwar Adnan Mohamed Saleh, a Palestinian, and Imad Eddin Barakat Yarkas, from Syria.
In 1995, Saleh left Spain suddenly, moving to Peshawar, Pakistan, where he began to work with the fledgling organisation that would become al-Qaeda. He helped move Muslim militants across the border into Afghanistan for training in the terrorist camps.
Yarkas's Madrid phone number was found by the German police in the Hamburg apartment believed to have been used by some of the hijackers, Judge Garzon's order says. Yarkas also listed Atta's phone number in his contact book.