I should point out that the people detained in Madrid are linked to having sold the mobile phone and fake phone card used as a timer in the backpack bomb that didn't go off, so this isn't precisely ironclad proof of an Al Qaeda job.
The left is trying to take full advantage of the situation; there was a "spontaneous" demonstration--some of the signs looked surprisingly professional, but then again they may be left over from some other demo--in front of the PP headquarters in Madrid, that drew at least 500 and maybe 3000 people accusing the Government of lying and of failing to appease Islamic terrorists. Supposedly this demo was organized by mobile phone, which just isn't the good old committee-and-bureaucracy let's-sing-the-Internationale Old Left we all know and love. TV 3 is making a big deal out of this. The other stations aren't paying it nearly as much attention.
Well, we'll see how this affects tomorrow's elections. I personally am going to wager that nearly everyone who is going to vote has his mind pretty much made up, and that this terrorist mass murder isn't going to greatly affect how people vote. It will just make both sides more partisan.
Alfredo Perez Rubalcalba from the Socialist Party just stated at a televised press conference that Spaniards "deserve a government that doesn't lie to them". This is politicizing the massacre, of course, not to mention illegally campaigning on the last day before the election, not to mention calling the Prime Minister and his Cabinet liars with no evidence. (In Spain it's not legal for political parties to campaign on the day before election day, dubbed the "day of reflection".)