WASHINGTON (AP) — 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.

The investigation was one of many that the task force had taken up, and the memo shows that Bloch frequently differed with investigators about which cases to pursue.

For example, he asked the task force to broaden its investigations into the fired prosecutors and into whether federal agencies received political briefings from the White House to boost GOP electoral fortunes. But he shut down an investigation into whether the Justice Department was hinging its hiring decisions on job applicants’ political affiliations.

An attorney for Bloch, who himself is under a federal investigation, declined comment. But a person familiar with the origins of the POGO draft document said the decision to not pursue Siegelman or other cases stemmed mostly from a shortage of time and resources. The person spoke on condition of anonymity because of the ongoing investigation.

Siegelman, a Democrat, said the memo suggests further political interference in his case and reiterated his call for the Justice Department to appoint a special prosecutor to take up the matter.

“The question is who told them to shut it down,” Siegelman said Wednesday when told of the memo. “Why would you start an investigation and let it proceed and then shut it down? The logical conclusion is that somebody intervened and told them to shut down the investigation.”

Siegelman has long claimed that Republicans engineered his prosecution on bribery and other corruption charges to kill his chances for re-election, a claim repeatedly denied by federal prosecutors. His attorneys requested earlier this year that the Justice Department appoint a special prosecutor to investigate whether White House appointees in Washington, including former Bush adviser Karl Rove, influenced the case. Rove also has denied any involvement.

The Special Counsel’s office is an independent agency charged with investigating unlawful political activity by government employees and ensuring that government whistle-blowers are not subjected to reprisals.

The January memo is a summary of the task force’s activities and recommendations since it was formed in May 2007. It says investigators expressed concerns about closing the Siegelman investigation before completing it. But the task force was “directed to not further investigate this case and to wait for further instructions.”

The memo says the task force still considered the case open and was requesting authorization to continue.

“I’m stunned by all this,” said Vince Kilborn, one of the former governor’s attorneys. “If an ongoing government investigation was shut down, I would say it’s potential obstruction of justice.”

FBI agents raided the office and Bloch’s home this week in an investigation into whether he destroyed evidence potentially showing he retaliated against staffers who opposed his policies.

Siegelman, who served one term as governor after being elected in 1998, was convicted in 2006 on bribery and other charges and sentenced to more than seven years in prison. He was recently released on bond pending appeal.