As evidence mounted to suggest that Al Qaeda was behind the train bombings that killed 200 people in Madrid last Thursday, governments across Europe have raised their security-alert levels for fear of further attacks against Washington's allies in its "war on terror."
But the persisting uncertainty over who was responsible for the massacre, and Spanish investigators' continuing pursuit of leads pointing to the Basque separatist group ETA, underscore doubts in some experts' minds about whether a broadly defined war on terrorism is likely to defeat individual terrorists. They fear that focus on the politically neutral tactic of terrorism may obscure the individual criminals using it.
"Terrorism is not an ideology or a political program but a tactic used for very different ends by very different groups," says Florentino Portero, a terrorism expert who heads the Strategic Studies Group, a think tank in Madrid. "You have to deal with different problems in different ways."
Three days after the worst terrorist attack on European soil in the continent's modern history, Spanish police were still struggling to reconcile contradictory pieces of evidence leading them in different directions.
A videotape found Saturday evening, made by a man purporting to be, or to represent, "the military spokesman of Al Qaeda in Europe" and claiming responsibility for the attack, provided further evidence for those blaming Islamic fundamentalists. Police had earlier arrested three Moroccans and two Indians they said were linked to the sale of a cellular phone found in one unexploded bomb, apparently intended to detonate the explosive.
ETA spokesmen have denied any ties to the bombings, and blamed Islamic fundamentalists.
At the same time, the fact that police arrested two ETA suspects last Christmas trying to carry out a train bombing that carried many of the hallmarks of Thursday's attack continued to trouble investigators. The explosives used, police forensic experts have concluded, were of a type ETA has used in the past.
The Moroccan authorities said Sunday they had identified the three Moroccans arrested Saturday, and that none had any known previous links with extremist Islamic groups.
In Madrid, a Moroccan woman who would give her name only as Amina said she knew one of the arrested men, Jamal, and doubted that he was guilty. "He is a normal warm guy, just trying to make a living," she said. "He has a telephone store. He has a Spanish girlfriend, a normal life. He is not an Islamist."
Public perceptions of who was to blame had immediate political implications in Spain, where many voters in Sunday's general elections were angry with the conservative government for having accused ETA immediately and been slow to acknowledge publicly any other suspects.
The ruling Popular Party, which had been leading in opinion polls, appeared vulnerable to charges that it was the Spanish government's enthusiastic support for the war in Iraq - opposed by 90 percent of the population - that had earned the deadly wrath of Islamist extremists.
"The government put itself in the war in Iraq even though no one here wanted it to, and now it is reaping what it sowed," said Cecilio Maezo Martin, walking near the scene of the attack at the Atocha rail station. "The government is manipulating the truth, it is deceiving us."
Such sentiments reveal that "the wounds of the Iraqi crisis are not healed," either in Spain or in other European countries where governments that supported the US attack on Saddam Hussein generally did so against strong public opposition, says Joachim Krause, a security expert at Kiel University in Germany.
If the tide of Spanish opinion turns strongly enough against the government to elect the Socialists, who have pledged to withdraw Spanish troops from Iraq unless they are mandated to stay by the United Nations, "that would be seen as a new appeasement," Professor Krause predicts.
The Madrid atrocity, and Al Qaeda's threats in recent communiqués to target other US allies, could further weaken other European nations' willingness to follow Washington's lead, says Dr. Portero: "The hope that by running away from a problem you can escape it is very human. Many people are thinking of not voting for the Popular Party because they believe this [attack] could have been avoided."
Underlying many Europeans' misgivings about the war on terrorism is a widely held feeling that the central event in that war so far - the invasion of Iraq - was based on false pretenses, such as the existence of weapons of mass destruction, or a link between Baghdad and Al Qaeda.
Also playing a role, however, is apparent mistrust of the way in which the US administration has cast its approach as a battle between good and evil, amalgamating Al Qaeda militants willing to sow civilian death and destruction with other, often very different groups.
"Every terrorist organization has to be looked at and dealt with on its own merits and against its own background," says Krause. "There are areas of commonality between them, such as the kinds of crime they commit and certain kinds of tactics, but those do not extend to strategies."
At the same time, he adds, some common responses are called for: Terrorist organizations of many different stripes use the same financial institutions to launder and transfer their funds, he says, "and most of them seek explosives, detonators, and other weapons on the same markets."
Some analysts, pointing to the way ETA members are known to have trained in the past in the Middle East with radical Arab groups such as factions of the Palestine Liberation Organization, suggest that common underground habits may have led to operational alliances in a new "terrorist international" reminiscent of the Popular Front for the Liberation of Palestine's joint attacks with the Badr-Meinhof gang, and the Japanese Red Army on planes and airports in the 1970s.
Such a development appears unlikely, however, to Portero, given the wide disparity between the goals of ETA, a Marxist-inspired organization fighting for Basque independence, and Al Qaeda, seeking to purify the world in line with its own interpretation of Islam.
"And anyway," he adds "if I were Al Qaeda, I would not seek a relationship with ETA, which is very weak and heavily infiltrated by police informers. It looks as though Al Qaeda can do what it wants to do on its own."
• Lisa Abend and Geoff Pingree contributed to this story from Madrid.