Denied terrorism fascinates me, because it is so counterintuitive. Traditionally, terrorism is a tactic used by a small group to force a large group -- the world, even -- into paying attention. The goal is to dramatize the cause as well as make people fear the terrorists.

Since Al Qaida, the old rule seems to have changed. There has still never been a claim of responsibility by Al Qaida for September 11. Osama bin Laden denies involvement with 9-11 as well as with other attacks. Instead, the group hides behind vague statements of support -- which conveniently allow their supporters to blame "Bush", or "the Jews" or whatever Great Satan is preferred. In most cases, shadowy front groups with vague connections to Al Qaida issue ambiguously worded claims tenuously linking Al Qaida (precisely what happened after the latest attack in Spain).

It's puzzling to me, but that seems to be a hallmark of al Qaida. It may involve the group's desire to intimidate as much of the world as possible, by building into its attacks a "now you see us, now you don't" mechanism so that no one knows which country is next.

The Basque group ETA, on the other hand, has a long history of attacks in which it has always claimed credit.

Prior to Thursday, ETA (Euzkadi Ta Askatasuna) had taken responsibility for more than 800 deaths in its decades-old campaign. Those were typically assassinations and smaller-scale attacks, the largest of which was a supermarket blast in Barcelona that killed 21 people in 1987.

Arnold Otegi, leader of Batasuna, an outlawed Basque party linked to the armed separatist group, denied it was behind Thursday's blasts and suggested they were the work of "Arab resistance" elements.

He told Radio Popular in San Sebastian that ETA always phones in warnings before it attacks. The interior ministry said there was no warning before Thursday's attacks, according to the AP.

I see no rational way that the latest attack advances ETA's agenda.

Al Qaida, though, relishes in people playing precisely these guessing games.

NOTE: Interestingly (according to the article), Spain is the only country to have indicted bin Laden for the 9-11 murders:

Spain served "as a place or base for resting, preparation, indoctrinating, support and financing" of al Qaeda, Garzon said in a nearly 700-page document.