MADRID, 11 March 2007 — Inside a red-brick courthouse here, defendants testified about the ease with which they obtained dynamite and traded it to alleged terrorists in exchange for hashish.

In other testimony, a top police inspector, his face concealed, told the court that Islamist militants chose Madrid for their first act of mass murder in Europe because Spain was seen as an easy target.

And another acknowledged that “we were always one step behind the terrorists.”

The government had hoped that the trial of 29 people accused in continental Europe’s deadliest terror attack would console Spaniards by showing them that the culprits had been brought to justice.

Instead, it has served as a reminder of how great the risks remain for a country that is still healing. Three years after bombs ripped through four Madrid train stations, killing 191 people and injuring nearly 2,000 others, Spanish officials and experts say the country is potentially in more danger now than ever before as extremist groups reorganize just beyond Spain’s southern coast.

Even as the trial began here in February, more arrests and prosecutions were being announced, and senior officials believe that radicals in Morocco and other parts of northern Africa, many with ties to Spain, increasingly take their cues from Al-Qaeda. Spanish authorities on Feb. 28 indicted Abdelilah Hriz, a 29-year-old Moroccan, as a principal author of the March 11, 2004, attacks, his fingerprints and blood allegedly found in an apartment where seven other key suspects blew themselves up to evade capture. Hriz was in custody in Morocco and will probably be extradited to Spain.

Investigators found DNA samples in the destroyed apartment that still have not been linked to any of the known perpetrators, indicating that additional suspects remain at large. Like Hriz, most of the accused in the train attacks are from Morocco or other parts of the Maghreb, the northwestern tier of Africa that also includes Algeria and Tunisia, a fact underscored by the faces and accents broadcast from the “11-M trial” (named for the date of the attacks). Nine of the accused are non-Muslim Spaniards.

Networks of Maghreb-based militants remain the most serious threat to Spain in terms of terrorism, law-enforcement officials said this week, charging that militants have set up a centralized command and training camps in southern Algeria and northern Mali, and have launched recruiting efforts in Spain.

Despite a pervasive climate of insecurity, said Myriam Fernandez Nevado, a Madrid-based political sociologist, “Spaniards have lived many years, decades, with terrorism, and they are very good at adapting, at rising from the ashes.”

Acrimonious partisan debate continues to swirl around the attacks and the investigation that followed. Some segments of the right-wing Popular Party, which was thrown out of office by voters days after the attacks, continue to insist that Basque separatists had a key role.

The argument, not backed by evidence, allows Popular Party members to deflect responsibility as a counter to those who say the party’s decision to send Spanish troops to Iraq made the country vulnerable to Islamists.

Polls show around a third of the Spanish public still unsure of who was behind the bombings.