From the Reuters:

Spain declassified intelligence reports on Thursday in a bid to show it told the truth about deadly train bombings it initially attributed to Basque guerrillas but which are now suspected to be al Qaeda-linked.

Street demonstrations accusing the government of hiding the truth on election eve were cited as a factor leading to the surprise victory of [the socialists]...

``Since the terrorist massacre, the government has communicated absolutely all the truth to public opinion, without hiding, manipulating or delaying any information,'' government spokesman and Labour Minister Eduardo Zaplana said.

The documents cover the period 3/11 to 3/14. They're online here, however, they're large PDFs and they're in Spanish.

There's also a chronology of events related to the bombing here. That too is in Spanish.

UPDATE: A partial translation is available. See this.