Well, “somebody” carry out an attack copied from the ones that happened in Italy in the 1970’s and 1980’s, and the Socialists, their friends in the Police and in the media and others, such as the Moroccans, made it look like a Islamic one, taking advantage of the worldwide concern after 9/11.
Zapatero himself was probably chosen as presidential candidate by the same or close associates to the ones that ordered the massacre, aiming at having someone mediocre enough to accept such a way of wining a National Election.
Cheers!