NEW ORLEANS — Grammy winning trumpeter Irvin Mayfield’s federal conspiracy and money laundering trial has been delayed a fourth time, pushed back to Jan. 21, 2020.

RELATED: David Hammer's previous stories on the Irvin Mayfield investigation 

Mayfield was indicted in December 2017 along with his longtime friend, business partner and band mate, Ronald Markham. They were initially charged with 19 felony counts for using their positions on the city's public library charity board to transfer more than $1.3 million in public library donations to the jazz orchestra Mayfield founded and that paid each of them six-figure salaries.

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The federal government added two superseding indictments in 2018, bringing the total charges against Mayfield and Markham to 24. Mayfield faces one of those counts alone and Markham faces another charge by himself.

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WWL-TV's exclusive investigation in 2015 and 2016 exposed the transfers to the New Orleans Jazz Orchestra, which was founded by Mayfield and led by Markham, as well as Mayfield's use of tens of thousands of Public Library Foundation funds on luxury hotel rooms, limo rides, liquor, meals and a $15,000 gold-plated trumpet.

The trial was originally set for October 2018, then pushed back to April 2019, then set for Sept. 30. Such delays are typical in white-collar criminal trials involving mountains of documentary evidence, but the latest delay is different.

This time, U.S. District Judge Jay Zainey agreed to delay the trial to January because he granted Mayfield and Markham an evidentiary hearing to possibly suppress evidence gathered by the Louisiana Legislative Auditor.

RELATED: Auditor secretly recorded Irvin Mayfield's partner; gave tapes to FBI

The Metropolitan Crime Commission alerted authorities about concerns about the New Orleans Public Library Foundation as early as 2013. After WWL-TV did a series of reports in May 2015 outlining the transfers from the Library Foundation to the jazz orchestra and detailing various public government grants received by the orchestra, the Metropolitan Crime Commission sent another letter to the legislative auditor urging it to investigate.

Investigative Auditor Brent McDougall did investigate, and court records indicate he secretly recorded interviews with both Markham and Mayfield. Markham’s attorney said she wants McDougall and FBI agent Courtney Lantto to testify to see if McDougall was acting as an agent of the federal government, arguing that Markham and Mayfield would not have spoken to McDougall if they knew he was coordinating with a criminal investigation against them.

The interviews all took place after WWL-TV had already reported that a grand jury was investigating possible crimes by Mayfield and Markham and some took place after they had already been served grand jury subpoenas, but Zainey ruled in June that there should be an evidentiary hearing because “neither defendant had reason to suspect that McDougall was helping out with the federal criminal investigation when they agreed to be interviewed.”

Zainey set that hearing for Oct. 2, which forced the trial itself to be pushed back.