SCRANTON, Pa. - Former state Senate Democratic Leader Robert Mellow pleaded guilty Wednesday in a public corruption case involving the misuse of his taxpayer-funded staff.

Mellow, who pleaded guilty to a federal conspiracy charge, faces up to five years in prison and a $250,000 fine when he is sentenced at a later date.

Mellow illegally used his Senate staff for campaign and fundraising between 2006 and 2010, and he filed a false 2008 tax return, according to a memo filed by prosecutors.

Prosecutors have said Mellow exhibited "willful blindness" while staffers were raising hundreds of thousands of dollars for the Friends of Bob Mellow campaign committee and for the Democratic State Senate Campaign Committee - all while on the public dime.

Mellow served four decades in the Senate and was one of the chamber's most powerful members when he opted not to seek an 11th term.

The 69-year-old has already paid a $21,000 fine for billing taxpayers to cover rental space for his district office in a building that he and his wife had a financial interest in, according to the State Ethics Commission. He's also paid nearly $32,000 in tax, interest and penalties stemming from the tax charge.

He said little Wednesday other than to briefly answer questions from the judge.