Zougam is well-known to Spanish police and is long suspected of having ties to Al-Qaeda.
The Associated Press reports today that Spanish police searched Zougam's Madrid apartment as early as a month before the 11 September 2001 attacks on the United States. In the search, police found a video of Islamic fighters in the Russian republic of Daghestan and phone numbers for three members of a Spanish-based Al-Qaeda cell.
That cell was led by another Spanish-based alleged terrorist, Imad Eddin Barakat Yarkas. Yarkas, also known as Abu Dahdah, is now in a Spanish jail on suspicion he assisted in the 11 September attacks. Those attacks, which killed some 3,000 people, have been blamed on Al-Qaeda.
Zougam was also the subject of antiterrorist probes last year in France and Morocco. Authorities say, among other things, Zougam was suspected of involvement in the Casablanca suicide bomb attack last May that killed at least 44 people, including the bombers.
The reports say he was never arrested for lack of evidence.
Word that a long-suspected terrorist may have been involved in the Madrid bombings has angered many in Spain, who wonder why Zougam was not under surveillance. Police say, in their defense, they do not have the resources to watch every terrorist suspect all the time.
Police, meanwhile, are stepping up the investigation and have invited other European intelligence and police services to take part. Karin von Hippel, a terrorism expert at Kings College in London, says it's logical to assume the Spanish network has ties across Europe.
"All these guys operate in an incredibly transnational way. They plan them in one country, they execute them in another, and so I'm sure they would have had connections with a number of European countries," von Hippel said.
It was not immediately clear if U.S. investigators are involved in the Madrid case. "The Wall Street Journal," in a report today citing unnamed officials, says the U.S. has assembled an antiterrorism task force that has not yet been invited in by Spain.
Von Hippel, who focuses her research on cross-border cooperation, says U.S. authorities are undoubtedly participating in the investigation at some level, even if that involvement has not yet been made public.
"I am sure [the U.S. agencies have been contacted], I'm sure they are involved as well. I mean, just because we haven't read it anywhere [in the newspapers doesn't mean that it's not happening]. I am sure they are talking to these guys regularly. They are talking to the [U.S. Central Intelligence Agency], the [U.S. Federal Bureau of Investigation], everybody. At that level there is amazing cooperation, actually," von Hippel said.
In the investigation, police appear to be backing away from an initial suspicion the bombings were the work of the Basque separatist group ETA.
The Spanish government, in the hours immediately after the attack, pinned the blame firmly on ETA, which has been waging a violent separatist campaign for decades.
The probe, however, turned toward Islamic militants on 13 March with the discovery of a videotape in a wastebasket near a mosque in Madrid.
On the tape, a man identifies himself as Al-Qaeda spokesman Abu Dujan al-Afghani. He says Spain was attacked because of its cooperation with the U.S. in Iraq and Afghanistan. He was reportedly speaking in Moroccan-accented Arabic.
Police later said they could not vouch for the identity or the claim. It wasn't immediately clear if Afghani has any ties to Zougam or the others. In today's media reports, the video is scarcely mentioned.