Parliament's investigation of the Madrid train bombings (search) opened Tuesday with a witness account of three suspicious men wearing wool caps on a warm spring day, their faces covered by handkerchiefs, at the station that was the starting point of the attacks.

One walked quickly toward the train carrying a bag, while the others stayed behind at a parked van.

"My blood ran cold. I thought it was a robbery," Luis Garrudo, a doorman in the town of Alcala de Henares, said.

Garrudo told the commission what he told authorities March 11: He directed police to the van that was found to contain a cassette tape with verses from the Quran, detonators and traces of explosives of the kind used in the attack.

It was the first big break in the case.

In all, 10 backpacks stuffed with dynamite and shrapnel exploded on four crowded trains heading to central Madrid during the morning rush hour, killing 190 passengers and bystanders, and wounding more than 2,000.

The attack is blamed on Islamic militants with possible ties to the international terrorist group Al Qaeda.

Of 50 people arrested, 16 remain in jail, including two who are believed to have put the explosives on the trains.

Garrudo, his face electronically obscured for security reasons on the live cable TV broadcast of the hearing, was the first of three people to testify Tuesday, among at least 35 overall.

The 16-member commission will interview witnesses and officials, and examine police documents and other evidence, to review what happened on March 11 and following days. On March 14, the Popular Party was upset in general elections that brought the Socialists to power.

The aim is to determine whether the emerging threat of Islamic terrorism might have been foreseen and counteracted; whether Spain is safer now that greater security steps have been taken; and what impact Europe's worst terror attack had on the election three days later.

Thirteen people, most of them police officials, were scheduled to appear before the panel this week. The investigation, similar to the Sept. 11 commission in the United States, is expected to last at least a month.

Garrudo testified police told him early in the afternoon of March 11 that "it was not ETA" responsible for the bombing, showing him photos of Arab suspects to try to identify the men he'd seen at Alcala de Henares train station, located east of downtown Madrid.

The government of then-Prime Minister Jose Maria Aznar (search) had insisted until hours later that the Basque separatist group was the probable bomber. Lawmakers and Spaniards want to know whether that apparent discrepancy affected the investigation or the election.

The commission has made front-page news since it was set up in May, most recently over which documents the government would declassify and who would be called to testify.

While declassifying some documents, the government of Prime Minister Jose Luis Rodriguez Zapatero (search) refused to declassify others, notably an intelligence report from October 2003.

It reportedly cautioned that a threat from Usama bin Laden to target Spain and other countries that deployed troops in Iraq during or after the U.S.-led invasion should be taken seriously.

The government won't declassify documents that contain information from foreign intelligence agencies, the public disclosure of which might provoke them to not cooperate with Spain's intelligence services.

The Popular Party sent 1,300 peacekeeping troops to Iraq despite massive opposition by Spanish voters. One of Zapatero's first policies was to remove them.

After Garrudo, the chief coroner for the Madrid regional government, Carmel Baladia, testified there was no evidence a suicide bomber was among the train victims.

Statements from prominent politicians were left for the final stage of the inquiry. Aznar has not been subpoenaed, but his Popular Party says he'll testify willingly if requested.