Washington ? The Justice Department’s watchdog office has opened an investigation into the arrest of an Oregon lawyer that was based on what turned out to be faulty FBI analysis of a fingerprint linked to the deadly terrorist attack last March in Spain.

Glenn Fine, the department’s inspector general, said the anti-terrorism Patriot Act might have been improperly used in the arrest of attorney Brandon Mayfield.

Mayfield, a Muslim convert and Kansas native, was arrested May 6 on a material-witness warrant after an FBI analysis concluded he was a match for a fingerprint found on a bag containing detonators like those used in the attacks on trains in Madrid that killed nearly 200 people and wounded 2,000.

A few weeks later, Mayfield was released after the FBI admitted it had made a mistake and that the fingerprint did not match Mayfield’s.

The inspector general’s investigation was disclosed in a semiannual report to Congress on potential civil-rights and civil-liberties abuses by Justice Department officials. A copy of the report was obtained Monday by The Associated Press, a day ahead of its release.

The Mayfield investigation is focusing on how the fingerprint error was made and also on a complaint by Mayfield that the “FBI inappropriately conducted a surreptitious search of his home … potentially motivated by his Muslim faith and ties to the Muslim community,” according to Fine’s report.

The Justice Department’s Office of Professional Responsibility also is investigating the actions of prosecutors in the Mayfield case.