WASHINGTON – The U.S. Office of Special Counsel last year shut down a previously undisclosed investigation into the federal prosecution of former Alabama Gov. Don Siegelman, according to an internal memo made public Wednesday.

The investigation was being conducted by a task force formed at the agency a year ago to pursue high-profile political investigations in Washington, most notably whether the White House played politics in firing U.S. attorneys. It began gathering information on the Siegelman case in September and was planning to request documents from the Justice Department in October before Special Counsel Scott Bloch ordered the case closed, according to the Jan. 18 draft memo, made public by the Project on Government Oversight, a watchdog group.