A lawyer and former US army officer who converted to Islam was arrested as a material witness in the investigation into the Madrid train bombings on March 11th, US authorities said.
Mr Brandon Mayfield was taken into custody yesterday by FBI agents, who also searched his home in the Portland suburb of Aloha.
It was the first known arrest in the United States with connections to the terrorist attacks that killed 191 people and injured 2,000 others.
Mr Mayfield (37) has not been charged with any crime, according to a police official in Washington D.C. His fingerprints were found on materials related to the Madrid bombings, said another police official.
A material witness warrant allows the government to hold people suspected of having direct knowledge about a crime or to allow time for further investigation into the witness.