Spanish police on Tuesday hunted Moroccan militants suspected of links to bombs that killed 201 people on Madrid trains and propelled the opposition Socialists into power at a general election.
Local media said police were looking for five fugitive Moroccans, part of a group of eight main Moroccan suspects.
Three are already in custody in connection with Spain's worst attack and the first suspected al Qaeda-linked strike in the West since the September 11 strikes on the United States.
But investigators cautioned against drawing any conclusions from the evidence gathered so far.
The investigation "is in its infancy. We have a long way to go," one law enforcement official said.
Spanish police, experienced with Basque separatist attacks, are considered expert at bomb analysis but have sought foreign help for what has become a complex international investigation.