-- earlier this year, by the Spanish Supreme Court -- maybe never would have happened if the voters in Spain hadn't sided with the Socialist opposition, after the Aznar government had tried to deflect blame on Basque separatists.
http://www.guardian.co.uk/world/2008/jul/17/spain.terrorismAccording to this link:
http://www.zimbio.com/Youssef+Belhadj/articles/4/SPANISH+CIVIL+GUARD+BOMB+SQUAD+FALSE+FLAG It is revealed that the man accused of supplying the dynamite used in the March 2004 Madrid train bombings was an informant who had the private telephone number of the head of Spain's Civil Guard bomb squad. Emilio Suarez Trashorras, a miner with access to explosives, as well as an associate named Rafa Zouhier both regularly informed for the Spanish police, telling them about drug shipments. Trashorras began working as an informant after being arrested for drug trafficking in July 2001, while Zouhier became an informant after being released from prison early in February 2002. Shortly after the Madrid bombings, investigators discover that Trashorras' wife Carmen Toro has a piece of paper with the telephone number of Juan Jesus Sanchez Manzano, head of Tedax, the Civil Guard bomb squad. She and her brother Antonio Toro are also informants.
In short, Trashorras and Toro are patsies and the evidence indicates the Spanish Civil Guard bomb squad was behind the bombing and a phantom “al-Qaeda inspired” terrorist group was simply a contrivance designed to feed public hysteria...
There's probably more to it than that. The Wiki 'Madrid Bombing Controversies' page includes links to conservative and right-wing information sources that now blame the bombing on Socialists, with the help of elements from Spanish, French and Moroccan 'intelligence', and the Basques.
What gets lost in the shuffle is that the Spanish Supreme Court basically cleared Al-Qaeda, itself, of any guilt for the bombing, and shifted it to an "Al-Qaeda-
inspired" attack...