OK, so here's what we have about the Spain thing:

ETA wanted to attack before the elections, and in December a similar ETA attack (also on the train system) was foiled. And the explosives were Spanish-made and similar to things ETA has used before.

BUT.

ETA usually gives a warning and claim of involvement, neither of which they did this time. On the contrary, they deny involvement. The scale of this attack is also much larger than anything they have ever done. And U.S. officials don't think they could do it alone, even if they were involved.

Further, synchronized attacks are a hallmark of al-Qaida. A van with detonators and an Arabic tape was found along the same commuter line which was bombed. And the explosives, although similar to those of ETA, are more modern. Also, a claim has been received in the name of al-Qaida, even though the reliability has not yet been proven. Plus, al-Qaida obviously has the motive - Spain is a key U.S. ally.

So, to get into the psychology of it - ETA could be denying it simply to mess with people's heads, because they know there's another scapegoat, or al-Qaida could be claiming it because they WISH they had done it, and they're trying to 'keep their threat alive', so to speak.

So I'm not sure what to think...