A key suspect in the Madrid terror attacks came under close scrutiny from law-enforcement and intelligence officials in at least three countries last year after bombings by Islamic militants in the Moroccan city of Casablanca, European law enforcement officials said Tuesday.

Officials said Jamal Zougam, a suspect in the train bombings last Thursday in Madrid, had been investigated and questioned last summer by law-enforcement officials in Spain, who received requests for information about him from both Morocco and France, the officials said.

Moroccan officials said they had uncovered ties between Mr. Zougam and several Islamist radicals who have been jailed since the May 16 Casablanca bombings. Spanish officials also opened their own inquiry into that attack because four Spanish citizens had been killed.

Mr. Zougam was arrested last Saturday along with two other Moroccans and two Indians after investigators traced a cellphone that was part of an unexploded bomb recovered from one of the destroyed trains.

Despite the attention Mr. Zougam received from the three governments after the Casablanca bombings, and the discovery of his ties to several important Qaeda figures, two Spanish officials said they had been unable to develop enough evidence to charge him with any crime. One of the officials said investigators eventually eased off their scrutiny of Mr. Zougam, simply because they had so many other suspects to monitor.

"There wasn't any physical surveillance of him, but there was an investigation," one of the officials said. "There was not enough evidence to move against him for the Casablanca matter."

Although it is not clear that any of the governments mishandled the case, the disclosures raise questions about the effectiveness of both their intelligence efforts and the antiterrorism cooperation among them.

"Morocco informed the Spanish that he went to Spain and that he was a quite dangerous person," a Moroccan official in Rabat said Tuesday evening. "There was no evidence against him in Morocco, but they asked Spain to investigate him."

Spanish counterterrorism officials are still uncertain what role Mr. Zougam, 30, might have played in the Madrid attacks last week, officials said.

Two survivors of the attacks have since told the police they think that they saw him on one of the trains, but one official said investigators remained skeptical of the witness accounts.

Nor did officials ever determine whether Mr. Zougam had any role in the Casablanca attacks, in which 12 suicide bombers and 32 other people were killed in synchronized strikes against targets that included a Spanish social club.

The Spanish inquiry into the Madrid bombings moved ahead slowly on Tuesday, officials said, as the police sought at least six more men, all of them apparently Moroccans, suspected of some involvement in the bombings last Thursday of four commuter trains in which 201 people were killed.

Tuesday evening, Spanish police agents spent more than an hour inside one of the two cramped storefront cellphone shops where Mr. Zougam had worked with Mohammed Chaoui, 34, who was said by friends to be his half-brother and who was arrested with him. The agents went into the store and came out leading a tall, handcuffed man whose head was covered with a dark hood.

Both Spanish and Moroccan officials noted that although Mr. Zougam had been linked to three important figures in the Casablanca bombings, he had never been conclusively tied to the attacks themselves.

After the Casablanca attacks, Moroccan officials said they quickly determined that Mr. Zougam had been in Morocco only weeks before. A senior Moroccan official said they also knew that he had "close relations" with an important suspect in the case, Abdelaziz Benyaich, a Moroccan who had fought with jihad groups in Bosnia and in Chechnya and Dagestan, Russia.

Other officials said Mr. Zougam was also close to Mr. Benyaich's brother, Salaheddin, a one-eyed Qaeda militant known by his nom de guerre, Abu Mughen.

Abdelaziz Benyaich was arrested that June in southern Spain and prosecuted by the Spanish investigative magistrate Baltasar Garzón on charges of belonging to a Qaeda cell. His brother, also wanted in Spain, was arrested in Morocco and charged in connection with an alleged plot to blow up a French oil refinery, officials said.

In Spain, Mr. Zougam was questioned in August at the request of French officials investigating the claims of Pierre Richard Robert, a French jihadi who also implicated the Benyaich brothers. Although the search of Mr. Zougam's apartment turned up Islamic militant books and videotapes, along with the phone numbers of several figures in a Madrid-based Qaeda cell, Mr. Zougam was not charged.

As far back as 2001, according to Spanish court documents, Spanish telephone intercepts showed Mr. Zougam in contact with the accused leader of that cell, Imad Eddin Barakat Yarkas, who was charged with assisting the hijackers in the Sept. 11, 2001, attacks in New York and Washington.

Other Spanish intelligence information shows that Mr. Zougam was known to have met in the summer of 2001 with Mohammed Fazazi, the spiritual leader of Salafia Jihadia, the Moroccan-based militant group accused of carrying out the Casablanca bombings, according to confidential Spanish court files obtained by Jean-Charles Brisard, the chief investigator in a lawsuit by relatives of victims of the Sept. 11 attacks.

Mr. Fazazi, an imam from a prominent religious family in Morocco, preached radical sermons at Al Quds mosque, once frequented by the Sept. 11 hijacker Mohamed Atta.

In addition to the three governments that had examined Mr. Zougam, Britain is now investigating whether he had contact with militants there.

Based on documents recovered in the search of Mr. Zougam's apartment, a senior British official said Tuesday, British counterterrorism officials are investigating whether he visited London in recent years, possibly to see Abu Qatada, a jailed militant whom they describe as Osama bin Laden's "ambassador" to Europe.