After hundreds of arrests and various investigative hypothesis, it appears that Spanish authorities have finally identified the man who, at least initially, conceived the 3/11 Madrid train bombings. El Pais reported three days ago that a new Spanish police dossier reveals that Youssef Belhadj, a Moroccan who has been arrested in Belgium for his connections to the GICM (Moroccan Islamic Combatant Group), is the man who decided the day for the attacks.
According to the report, Belhadj chose March 11 as the day of the attacks on October 19, 2003, the day after al Jazeerah broadcasted a tape where Bin Laden threatened Spain for its involvement in Iraq. That day Belhadj also bought a new Belgian cellphone, providing a false name and ?March 11, 1921? as his date of birth . Knowing that the Spanish elections would have taken place in March, but ignoring the exact day, he decided for the 11, so that the Madrid attacks would have taken place exactly two years and a half after those in the United States.

A senior GICM member, Youssef Belhadj, was arrested in Belgium a week after the Madrid bombings and charged with membership in a terrorist organization. Released in July on bail, he was arrested again in February 2005 after Spanish authorities issued an international arrest warrant for him. Spanish magistrates believe that Belhadj, who had left his sister?s Madrid apartment shortly before the train bombings, had been one of the masterminds behind the attacks?indeed, they think he is Abu Dujan al Afgani, the mystery man who claimed responsibility for the bombings in a tape found two days after the attacks near a Madrid mosque. Belhadj?s sister Safia, her husband Allal Moussaten, and the couple?s two sons have also been arrested by Spanish authorities for their involvement in the train bombings.

UPDATE 8/9 by Andrew Cochran: "Robert Wesley, a
counterterrorism expert based in Vienna, wrote us this morning with the following information: "(T)here was also reporting in El Pais concerning the communication methods of the cells. They used an email account (not a free account I believe) set up by a third party in which the password and username were disseminated to members of the group. The date of birth recorded for the creator of the account was 11 March 2004. Members would log in and write a letter but would save it as a draft, the other members would log in, read the draft, erase it and write their own draft email, never sending the email."

Lorenzo responded as follows: "Yeah it is called 'dead drop box.' It was used by Mohammed Momin Khawaja, a Canadian man arrested in March 2004, and by a cell of Pakistani militants in London accused of planning to bomb unspecified targets in Britain. A message is written and simply saved in the 'draft' box of an e-mail account. Various people in different parts of the world who have the password of the account can read the message without its ever being sent. Didn't know the Madrid folks did that too. Very interesting, thanks."

http://counterterrorismblog.org/2005/08/finally_madrids_mastermind_upd.php