Attorneys for Ray Nagin told a federal appeals court panel Monday that a faulty jury instruction tainted at least nine of the 20 criminal charges on which the former New Orleans mayor was convicted and imprisoned last year.

Nagin’s federal public defenders also argued that U.S. District Judge Helen “Ginger” Berrigan improperly levied a $500,000 forfeiture against Nagin as a “personal money judgment” that illegally obligates him to pay money he doesn’t have once he completes his 10-year prison sentence.

Nagin, 59, remains behind bars at a federal prison in Texarkana, Texas. He did not appear for the oral arguments before a panel of judges of the 5th U.S. Circuit Court of Appeal.

One of his attorneys, Jordan Siverd, argued that Berrigan issued an improper instruction that allowed the jury to convict Nagin on nine counts of “honest services” fraud, or depriving the public of its right to his honest services.

He said the jury should have been told that Nagin could be found guilty of accepting those bribes — nine $12,500 payments that Nagin received under a post-mayoral consulting contract with developer Frank Fradella — only if prosecutors could show that the money actually influenced Nagin’s behavior in office.

Fradella made the payments after Nagin left office.

The allegedly faulty instruction — which Nagin’s trial attorney, Robert Jenkins, did not contest at the time — may also have tainted the jury’s verdict on a conspiracy count and other charges in a 21-count indictment issued in January 2013, Siverd argued.

He pointed to a 2010 U.S. Supreme Court ruling that narrowed the scope of a law that is often used to prosecute political corruption but has come under fire as too vague. The high court’s ruling in that case, U.S. v. Skilling, limited the future application of “honest services” fraud charges to “bribes and kickbacks.” Nagin’s case did not meet that bar, according to his appeal.

Nagin argued at his trial that several of the payments he accepted — from Fradella and businessman Rodney Williams, for instance — made no difference because his power over city contracts was limited. The City Charter, public bid laws and a veto-proof City Council majority left him no ability to choose favored vendors, he argued.

Berrigan wrongly told the Nagin jury that “it is not a defense to claim that a public official would have lawfully performed the official action in question even without having accepted a thing of value,” according to the appeal.

“You have to show the reason for the official act was the payment,” Siverd told the panel.

It is unclear whether Fradella ultimately benefited at all from his monthly consulting payments to Nagin or the tens of thousands of dollars worth of granite that Fradella gave to a company owned by Nagin’s sons. None of Fradella’s more ambitious development plans in the city — deals he hoped to land with the help of the mayor — panned out.

Assistant U.S. Attorney Richard Pickens, part of the team of federal prosecutors who tried Nagin, argued that what matters legally isn’t whether the government proved that Nagin ever intended to wield his mayoral power for Fradella, only that he agreed to do so.

“You need the quid pro quo, and we have that in this case, over and over,” the prosecutor said.

Fifth Circuit jurists Fortunato Benavides, James Dennis and Gregg Costa heard the case Monday, with Benavides joining silently by phone. Only Costa raised questions during the 40-minute hearing, expressing skepticism at Nagin’s argument.

“It seems like clearly a misuse of office to receive these payments,” Costa said. “It just seems like classic ‘honest services’ fraud.”

The nine counts at the heart of Nagin’s appeal stem from payments totaling more than $100,000 that he received from July 2010 to March 2011. Federal prosecutors described the transfers to the jury as payoffs dressed up as a consulting contract for Nagin after he left office in 2010.

As mayor, Nagin went to bat for Fradella on several fronts, including holding a news conference at which Fradella could trumpet his development plans and helping Fradella shore up his bona fides with financiers, the government argued. Nagin also flew to Baltimore for a meeting aimed at igniting a massive redevelopment project for a former Entergy plant near the Mississippi River at Market Street. Fradella had been angling for a piece of the project.

The $12,500 payments came later, through a contract with Green Energy Management Services Inc.

“There was no evidence (Nagin) was going to do any of this without the payment,” Pickens told the panel. “This was a classic, ‘You scratch my back, I’ll scratch your back.’ ”

Nagin’s attorneys argue that he did in fact perform consulting work in return for the $12,500 payments, further complicating the jury’s decision on his guilt.

The claim that the “honest services” statute was misapplied forms the centerpiece of Nagin’s appeal. But Siverd argued that the incorrect jury instruction also undermined several money-laundering and bribery counts on which he was convicted, as well as the over-arching conspiracy charge.

Nagin’s appeal also says Berrigan erred when ordering him to pay $501,201. It says she misused the criminal forfeiture statute to saddle Nagin with a lifetime of personal debt, rather than seeking to seize the actual fruits of his criminal actions.

“I don’t think there was anything left to seize” upon Nagin’s conviction in February 2014, Siverd said.

Berrigan ruled in September that the former mayor was indigent and eligible for a public defender after Nagin reported having only $23.65 in his checking account.

Pickens argued there was nothing wrong with Berrigan’s forfeiture order.

Nagin is slated to be released from federal prison in 2023.

The panel did not say when it will rule on the appeal.

Follow John Simerman on Twitter, @johnsimerman.