Madrid, Spain ? Abu Musab al-Zarqawi, a Jordanian linked to al-Qaida and suspected of heading a terrorist network in Iraq, is now believed to have been the brains behind the deadly Madrid railway attacks, a French private investigator said Friday.

Investigator Jean-Charles Brisard said Spanish officials told him some suspects held in the March 11 attacks were in contact with al-Zarqawi as recently as a month or two before the bombings, which killed 190 people and wounded more than 1,800.

“They believe today he was the mastermind,” Brisard, who is probing the Sept. 11, 2001, attacks on the United States, said in a telephone interview from Geneva, Switzerland.

The Spanish Interior Ministry declined to comment on his assertions. “The investigation is at a critical stage,” a ministry official said, speaking on condition of anonymity.

Late Friday, a Spanish radio station reported that police think they have located the house where the bombs were built. Investigators found detonators and traces of dynamite inside the house near Alcala de Henares, 20 miles northeast of Madrid, radio network Cadena SER reported.

It said the attackers were believed to have used the building to prepare the explosives and stuff them into knapsacks. The investigators found the house a week ago, according to the report.

Brisard’s comments came as the probe spread to Germany, a key staging ground for the 9-11 attacks on New York and Washington.

German police raided an apartment in Darmstadt where a Moroccan suspect arrested Wednesday in the Madrid train bombings stayed briefly last year. The 28-year-old man is suspected of membership in a foreign terrorist organization, a prosecutor said.

But German officials said they had no evidence that the Madrid attacks were planned or prepared in Germany.

In Spain, authorities announced another arrest Friday, and a judge charged a 12th suspect in the case.