Here's more information on the white van found outside Madrid (link):

SPANISH police last night established a direct link between the white "Koran van" and an unexploded train bomb in Madrid...

Investigators found a mobile phone in the van - and have proved a link to another phone found in a sports bag packed with explosives on the train that was ripped apart at El Pozo station...

But sources close to Spanish authorities said they were still keeping an open mind as the Koran tape could have been planted as a smokescreen...

Last night a witness came forward to say he had seen three indivduals emerging from the van with their hair and mouths masked.

In Madrid, theories were gathering pace that ETA could have been working in league with Islamic terrorists...

But the holdall that did not explode contained explosives often used by Basque terrrorists...

A caller said [ETA] "has no responsibility whatsover for the Madrid attacks". In the past it has been ready to admit its involvement...

Perhaps it wasn't meant to be this deadly, or perhaps their attempts to warn about the bombs beforehand hit a snag. They probably wouldn't take credit in those cases.

See earlier posts here and here.

There's also more on recent ETA activity in 'Recent incidents steer suspicion toward ETA' (msnbc.msn.com/id/4516956).

There's a Wiki on the attack (March_11%2C_2004_Madrid_attacks).

UPDATE: The NYT report 'Officials Still Divided on Whom to Blame for Madrid Bombings' (link) has no new information except for this: "The ["Koran van"] also contained some documents in Arabic and an audiotape of readings from the Koran that one official said referred to the education of children."

The van appears to have been definitely linked to the bombing. While Arabic tapes are probably quite easy to obtain in Spain, the documents might be more difficult to get. If they're something that's easy to obtain that's one thing. But, if they're handwritten or custom-printed documents it might favor involvement by someone who speaks Arabic. Note, however, that the van was stolen, so they might have belonged to the van's owner.