Grammy-winning jazz trumpeter Irvin Mayfield and his longtime friend and business partner Ronald Markham face new accusations related to charges they illegally siphoned off $1.4 million in New Orleans Public Library Foundation money, much of it to themselves.

A superseding indictment handed up Thursday marks the second time that federal prosecutors have added charges and additional details to the original 19-count indictment brought against the two men last year.

Thursday’s charging papers add only one criminal count — accusing Markham of making false statements — bringing the total number of charges against the two musicians to 24.

But the new indictment also adds new allegations under a conspiracy charge that accuses Mayfield and Markham of numerous attempts to deceive library foundation auditors.

Mayfield is now accused of asking a friend who worked at a local church to hold about $70,000 in library foundation funds in a church bank account. Mayfield allegedly told the friend he was “trying to avoid moving the funds to an organization of which he was a board member.”

Mayfield and Markham also are accused of lying to foundation auditors about a money transfer to the Youth Rescue Initiative, another organization in which Mayfield was involved.

The new indictment also accuses the two men, who were given nearly unfettered control of the library foundation's money, of doctoring board minutes in late 2013 to change “line items and dollar amounts” of foundation funds transferred to Mayfield’s New Orleans Jazz Orchestra.

Mayfield and Markham, who each at one point served as president of the library foundation's board, then allegedly used those altered board minutes to justify the transfers to other board members.

The newly added charge against Markham alleges that he lied to the FBI, claiming he was ignorant about who altered the board minutes.

Markham's attorney, Sara Johnson, said the new charge is based on a theory that prosecutors had before either man was first indicted.

"I can't think of a reason why they chose not to charge it (until now) other than to keep the story in the news," she said Thursday. 

The new indictment against Mayfield, 40, and Markham, 39, appears to argue that the two men were well aware that they were covering up what prosecutors in U.S. Attorney Peter Strasser’s office suggest was a well-crafted ploy to enrich themselves through library donations.

Both men pleaded not guilty to prior indictments in the case and have remained free on bail.

Mayfield drew praise in the city for his musical artistry and his promotion of the city after Hurricane Katrina, before investigative reports by WWL-TV sparked a federal investigation into his use of the library foundation's funds, which donors had intended to support the city's public libraries.

The feds allege that Mayfield and Markham, a pianist, stole from the foundation, where they sat as board members between 2011 and 2013.

Prosecutors claim Mayfield lived a jet-setting life with foundation funds, including expensive stays at luxury hotels in New York City. Mayfield, though, has claimed poverty in court, telling pre-trial services officials that his monthly bills exceed his roughly $800 a month in income as a musician.

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The two men are both charged with one overarching conspiracy count, six counts of wire fraud, a count of conspiracy to launder money, 13 counts of money laundering and aiding and abetting, and one count of obstruction of justice.

Mayfield alone faces an additional charge of mail fraud, and Markham faces the new count of making false statements.

The most severe charges carry a maximum 20-year sentence for each man.

Federal Public Defender Claude Kelly, who is representing Mayfield, has alleged that federal prosecutors tainted the case against his client by leaking information from grand jury proceedings to a WWL-TV reporter.

Follow John Simerman on Twitter, @johnsimerman.