Bombs were Spanish-made explosives
As investigators learned more about the bombs that ripped through trains killing and maiming, millions of people across Spain gathered in chilly rain to protest the terror attacks and mourn the victims Friday.
"It seems like the sky is crying," said one woman.
Suspicion for the coordinated terror attacks has fallen on Basque separatist group ETA and Osama bin Laden's al Qaeda terrorist network.
The 10 backpack bombs, carried aboard four trains and detonated almost simultaneously at three stations, killed 199 people and wounded more than 1,450.
Authorities said they found and safely detonated three more bombs, apparently set on timers to explode later, when rescuers and security forces were on the scene.
The explosive used came from inside Spain and is similar to explosives used in previous attacks by ETA, according to Glenn Schoen, a security analyst who has seen the latest police analysis.
On the other hand, the copper detonators used in the backpack bombs were more sophisticated than the aluminum detonators previously used in bombs linked to ETA, said Schoen, who has worked with Spanish police on train security.
The preliminary analysis determined the explosive is a type of dynamite called ECO, manufactured in Spain and normally used in construction and mining, Schoen said.
Schoen -- director of analytical services at TranSecur in Washington -- was in Madrid last week inspecting railroad facilities as part of his work with Spanish police.
Interior Minister Angel Acebes insisted ETA remained the prime suspect in Thursday's attacks despite the group's denials and regardless of some evidence that seemed to indicate Islamic terrorists could have been involved.
Acebes said ETA, which has waged a 36-year terrorist war for a separate homeland, had to be the "main line of investigation."
"Nobody has any doubt that ETA wanted to attack before the general elections," Acebes said.
ETA is designated a terrorist organization by the United States and the European Union.
Attacks blamed on or claimed by ETA over the last three decades have killed 800 people in Spain -- the most deadly of which was a 1987 supermarket bombing that killed 21.
Acebes pointed out that Spanish authorities had last month stopped a van carrying 500 kg of explosives on its way to Madrid, and in December stopped a similar attack, with multiple bombs that were to go off simultaneously, on the commuter train system. Both incidents involved ETA.
"How is it possible that after 30 years of attempts of ETA, they are not going to be priority suspects in this investigations?" he asked.
But, echoing remarks from President Jose Maria Aznar earlier, Acebes said that no line of investigation would be ignored.
The interior minister said that investigators had found an intact bomb backpack aboard one of the trains. Inside, he said, they found a Spanish-made explosive reinforced with shrapnel, a detonator with a cell phone and a timer. The cell phone, he said, opened up "new lines of investigation."
Acebes said the explosive found in the bag was not of the type usually used by ETA, but was instead a more "modern" version of ETA's usual dynamite.
But in anonymous calls Friday to Basque media outlets, ETA apparently vehemently denied involvement. Basque TV, which is owned by the Basque regional government, received one of the calls, the station told CNN, and the newspaper Gara -- where ETA frequently publishes its claims of responsibility for attacks -- told CNN Espaņol it also had received a call.
ETA does not generally call Basque TV.
U.S. military and intelligence officials said they doubted ETA, if it were responsible for the attacks, could have carried them out alone, a Pentagon official told CNN.
Those officials pointed to the synchronized timing of the attacks as a possible key to which group might be responsible, a Pentagon official told CNN.
This official emphasized that as yet not enough information was available to draw any kind of definitive conclusion.
Near simultaneous attacks are a hallmark of al Qaeda, the U.S. officials pointed out. They also pointed out that ETA attacks are nearly always accompanied by a warning and a claim of responsibility, neither of which happened Thursday. In addition, the scale of the attacks was much larger than anything ETA has previously carried out.
And then there was the discovery of a van -- containing seven detonators and an Arabic tape of Koranic teachings -- in the eastern suburb of Alcala de Henares, located on the same commuter line that was attacked Thursday.
Spain has been a key ally of the United States, particularly in the war with Iraq, and the terrorist group al Qaeda has previously threatened any country so allied.
Meanwhile, an Arabic-language newspaper in London said it received an e-mail claim of responsibility in the name of al Qaeda from the Abu Hafs al-Masri Brigade.
However, intelligence sources have consistently told CNN that the Abu Hafs al-Masri Brigade does not speak for al Qaeda, and is unreliable because of past claims that turned out to be false.
Aznar pledged on Friday to hunt down the bombers as Spain marked the first of three days of mourning for the victims of the blasts.
"We will bring the guilty to justice," he said Friday. "No line of investigation is going to be ruled out."
Two million people took to the streets of Madrid, police say, filling elegant plazas with seas of umbrellas.
A similar scene filled the streets of Bilbao, the largest city of Spain's Basque region, and in Barcelona.
Among those attending the rallies in Madrid were Italian Premier Silvio Berlusconi, French Prime Minister Jean-Pierre Raffarin, European Union President Romano Prodi and German Foreign Minister Joschka Fischer.
Aznar joined other senior officials outside the presidential palace to launch the three-day period of mourning.
"I think that Spanish people are showing again their strength, their solidarity, and the common effort in order to overcome the atrocities of pain and terrorism," Aznar said in remarks before the moment of silence.
"And all this defines us as a civilized, democratic and a strong nation."
Protests in Barcelona
Aznar said he had set aside 140 million euros ($171.2 million) for the families of victims, and the Spanish government called for massive protests against the violence Friday evening.
International outrage was quick in coming. France, across the Pyrenees border from Spain, lowered its flags to half staff.
In London, British Prime Minister Tony Blair said each generation had its wars to fight, but the war of this generation "is not a conventional war."
"It is fought by dangerous fanatics," he said. "They are terrorists without any mercy and without any thought."
In Washington Friday, President Bush and first lady Laura Bush laid a wreath at the Spanish Embassy to commemorate the solemn occasion.
"The bombings in Spain are a grim reminder that there are evil people in the world who are willing to kill innocent life," the president said. "The United States of America stands firmly with you as we work to make the world more peaceful and more free.
"The killers try to shake our world, try to shake our confidence in the future," he said. "The Spanish people will stand firm against this type of killing and the United States will stand firm with them."
The German parliament also held a moment of silence for the attacks' victims, as did the European Union. Italians held demonstrations to show solidarity with Spain.
The Madrid bombings were the second deadliest in Europe since World War II. Only the bombing of Pan Am Flight 103 over Lockerbie, Scotland, in 1988, killed more people than Thursday's attacks. The Lockerbie bombing killed 259 people on the plane and 11 on the ground.