Police investigating the Madrid terror bombings have arrested a Moroccan whose telephone number was found in the ruins of an apartment where seven suspects blew themselves up, the Interior Ministry said Saturday.

The man, whose name was not released, was arrested Thursday night in Parla (search), a town just south of Madrid, a ministry official said.

The suspect's telephone number was found in the wreckage of an apartment where seven suspects, including the suspected ringleader of the train attacks, blew themselves up on April 3 as police prepared to go in and arrest them, the official said.

The attacks on March 11 killed 191 people and wounded more than 2,000, and have been blamed on Islamic militants with possible links to Al Qaeda.

Eighteen people have been charged so far — six with mass murder and the rest with collaborating with or belonging to a terrorist organization. Six of the 18 have been released from jail but still face charges.

On Thursday, the FBI arrested an American lawyer, Brandon Mayfield (search), 37, in the United States as a material witness in the case.

Spanish officials say at least one of Mayfield's fingerprints were found on a plastic bag containing detonators of the kind used in the attacks. The bag was found in a van left near the station from which three of the four trains bombed on March 11 departed. U.S. officials said a single print of Mayfield's was found on the bag.

The newspaper El Pais (search) reported Saturday that Spanish investigators have serious doubts as to whether the print is Mayfield's. They have no record of him traveling to Spain recently, and experts found only eight points of similarity between the print and the one of Mayfield held in U.S. files because of his status as a former member of the Army. The FBI said it found 15 such points, El Pais said.

The Interior Ministry declined to comment on the report.