PORTLAND - FBI agents used provisions of the USA Patriot Act during their investigation last year of a Portland attorney who was wrongly jailed for two weeks on suspicion of involvement in the Madrid train bombings, according to a Justice Department letter.

The Patriot Act allows for covert searches of homes, without conventional search warrants.

Brandon Mayfield was jailed last May after his fingerprint was incorrectly matched to one found on a bag of detonators near the scene of the Madrid attack, which killed 191 people. He was released after the FBI admitted its mistake.

Mayfield, a Muslim convert, has filed a lawsuit against the U.S. government, contending his rights were violated by his arrest and by the investigation against him. He also contends the Patriot Act is unconstitutional.

While preparing the case, Mayfield's attorneys sent a letter to the Justice Department in February seeking an order compelling the U.S. Attorney General to inform Mayfield about any electronic surveillance that was conducted during the investigation and any secret searches.

In response, the Justice Department sent a letter acknowledging FBI agents searched Mayfield's house under provisions of the Patriot Act.

The letter provides new details about the investigation against Mayfield, stating that agents seized three hard drives, 10 DNA samples preserved on cotton swabs and took 335 digital photographs of personal effects in his home.

He also was the target of "other physical searches," the letter states, without elaboration.

In court papers filed Tuesday in U.S. District Court in Portland, Mayfield's attorneys called for the government to disclose more details about the search. The attorneys are seeking information on how the DNA samples were analyzed, where wiretaps were placed, copies of existing transcripts and information on the specific images taken.

Calls to the Justice Department in Washington, D.C., and to the U.S. Attorney's office in Portland late Tuesday were not returned.

Michael Greenberger, a former Justice Department official in charge of counterterrorism, said he believes the Justice Department letter is the first time the U.S. government has acknowledged using the so-called "sneak and peek" provision of the Patriot Act.

"The whole purpose of sneak and peek is that no one ever knows that it has been done. So this appears to be the first time a citizen has had the legal forum to inquire - and to get a disclosure from them," said Greenberger, director of the Center for Health and Homeland Security at the University of Maryland.