Convicted Ponzi schemer Tom Petters claims his former attorney withheld a government plea offer—and he’s now asking a court to throw out his 50-year prison sentence.

Petters claims that his prior attorney, Jon Hopeman, never told him about a pretrial offer from prosecutors to cap his punishment at 30 years in exchange for a guilty plea, according to media reports.

In court documents filed Friday, Petters said the court should regard his sentence as “unlawful and unconstitutional,” according to a report by the Star Tribune.

Petters asked for a new sentencing hearing to be convened at which he would be allowed to plead guilty to prosecutors’ pretrial offer and receive a reduced sentence, Businessweek reported.

Petters was convicted in 2009 of 20 counts of fraud, conspiracy, and money laundering, and he received his 50-year prison sentence in 2010. Petters reportedly claims that Hopeman didn’t relay a pretrial offer that came in a few weeks after the Ponzi scheme was uncovered in September 2008.

Friday’s motion was reportedly filed in federal court by Petters' new attorney, Steven Meshbesher, another prominent Minneapolis defense attorney.

Meshbesher’s filing claims that, “but for Mr. Hopeman’s ineffective assistance, defendant Petters would have received a far shorter sentence than currently imposed,” according to Businessweek.

Hopeman told Businessweek by e-mail: “No comment except I wish Mr. Petters the best.”

Last year, Petters asked the U.S. Supreme Court to review his conviction, although the Supreme Court denied his petition. That move came after Petters' appeal was denied by a lower court: A three-judge 8th U.S. Circuit Court of Appeals panel upheld Petters’ conviction and sentence, as did the full 8th Circuit Court. Petters’ appeal to the Supreme Court argued that the trial judge had barred the defense from presenting evidence about Larry Reynolds—a prosecution witness that Petters’ attorneys said has a long criminal history and perpetrated the fraud without Petters’ knowledge.

Of the 13 people charged in relation to the Petters fraud, Petters and James Fry were the only ones who did not plead guilty to the charges against them.

Petters broke his silence last year, speaking from prison in an exclusive interview with Twin Cities Business Editor in Chief Dale Kurschner. To read the resulting feature story, click here.