A Spanish judge has charged a Moroccan man suspected of planning the Madrid bombings with 191 counts of murder.
Hasan al-Haski is believed to have planned the Madrid train bombings
Hasan al-Haski, 41, was also accused of 1,000 counts of attempted murder and membership of an armed group.
Judge Juan del Olmo said he was a suspected member of the Moroccan Islamic Combat Group - also blamed for the May 2003 Casablanca bombings.
Three more men were arrested with Mr Haski in the Canary Islands last week, one of whom remains in custody.
Mr Haski, who denies the charges against him, was remanded without bail after the hearing at Spain's National Court.
The four arrested, all Moroccan citizens, are all believed to be members of the MICG, which is alleged to have links with al-Qaeda.
The men were allegedly setting up a logistical base on Spain's Canary Islands, off the coast of northern Africa.
Judge del Olmo's 29-page warrant said that another member of the same group recently arrested in France had quoted Mr Haski as saying that "his group
in Spain had carried out" the 11 March attacks in Madrid.
Reports say investigators also believe Mr Haski is the leader of a militant Islamic group which carried out the Casablanca bombings in 2003.
He has faced further questioning by Spain's top anti-terror judge, Baltasar Garzon, as part of a separate inquiry into the Casablanca attack.
Seventeen more suspects have been imprisoned on provisional charges in connection with the investigation into the Madrid bombing.
The Spanish Prime Minister, Jose Luis Rodriguez Zapatero, on Tuesday announced that a special security plan will be enforced in Spain over Christmas against possible terror attacks over Christmas.
The Casablanca attacks in May 2003 killed 45 people, including 12 suicide bombers.