A former Pennsylvania state Senate leader is being investigated for "federal-program theft, extortion, fraud, and money laundering," according to a federal appeals court opinion filed Wednesday.

The revelation is contained in an opinion by the U.S. Court of Appeals for the Third Circuit in Philadelphia, denying an attempt by retired Sen. Robert J. Mellow (D., Lackawanna) to recover evidence seized during a June 2010 raid of his home and district office in Peckville.

The opinion does not name Mellow, 67, as the target of the grand jury investigation being conducted by the FBI and the IRS out of Scranton, but refers to a warrant executed June 18. That's the day federal agents are known to have raided Mellow's home and district office.

Mellow's attorney, Sal Cognetti Jr., argued the appeal last month, according to newspapers in Wilkes-Barre. Cognetti could not be reached Thursday for comment.

Mellow, who left the Senate in January after 40 years in Harrisburg, told the Associated Press that he had not seen the opinion and had "no idea" whether he was under investigation.

The Inquirer reported last year that Mellow was the subject of a federal grand jury investigation concerning the rental of his district office in a building in Peckville.

The Senate spent $213,000 from 2001 to 2006 to rent Mellow's district office from a business half-owned by his then-wife, Diane, according to an Inquirer report. After the couple divorced, her share of the business went to Mellow, and he held it from 2007 until 2008.

At various times, people with ownership stakes in the building also included his longtime aide Gabriel J. Giordano and Giordano's wife, Celestine P.

Over the last few months, FBI agents have subpoenaed dozens of Democratic staff members, including ones from Mellow's Senate office.

At the time of the raids in June, federal agents confirmed only that they were conducting a joint investigation into "alleged illegal activities."

Mellow has repeatedly denied doing anything wrong.

The court rejected Mellow's appeal to have seized copies of his computer hard drives and other records returned to him, saying he was trying to suppress evidence before any charges were filed.

"The motion plainly sought not just the equitable return of property, but also the suppression of evidence - i.e., to prevent the government from using the evidence in criminal proceedings," Judge D. Brooks Smith wrote.

Mellow also wanted to unseal the search affidavit.

The appeals court declined to review a decision first issued by the U.S. District Court in Scranton siding with the government, which argued that unsealing the warrant could facilitate obstruction of the investigation by revealing what federal agents were seeking.

The government also maintained that the warrant would identify informants, disclose the names of people who might never be charged, and make public confidential grand jury and tax information, according to a legal filing.

Contact staff writer John Sullivan at 215-854-2473 or jsullivan@phillynews.com.