A U.S. appeals court on Tuesday expressed uneasiness with how a federal prosecutor invoked the civil rights movement in asking a mostly black jury to find five white employees of Bernard Madoff's firm guilty of helping him carry out his Ponzi scheme.

Questions by members of the three-judge panel of the 2nd U.S. Circuit Court of Appeals in New York suggested the court would likely uphold the 2014 convictions of the five employees of Madoff's firm.

But some members of the panel appeared nonetheless critical of the arguments made at the close of a six-month trial by the prosecutor, who a trial judge said made remarks that were "ill-conceived and unworthy" of his office's stature.

"This is the last thing the jury heard before it deliberates, so a rebuttal has to be handled in a responsible way," U.S. Circuit Judge John Walker said. "And I'm not sure it was."

The five employees were among 15 people who pleaded guilty or were convicted at trial in connection with Madoff and his firm, Bernard L. Madoff Investment Securities LLC.

Madoff is serving a 150-year prison term after pleading guilty in 2009 to running a scheme that cost investors an estimated $17 billion or more in principal.

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The five employees included former back office director Daniel Bonventre; portfolio managers Joann Crupi and Annette Bongiorno; and computer programmers Jerome O'Hara and George Perez.

On appeal, they cited as improper statements made during rebuttal arguments by a prosecutor, Randall Jackson, that called the defendants' arguments "ridiculous" and "absurd," and referenced movies including the "Godfather" series.

Jackson, who is black and is now in private practice, also asked jurors to approach their deliberations with the same "courageous approach" as Constance Baker Motley, a civil rights lawyer who became the first black woman federal judge in 1966.

The 12-member jury included six black jurors and one Latino.

"This is beyond the pale, and I think it was clear," said Andrew Frisch, a lawyer for Daniel Bonventre, the former back office director.

Assistant U.S. Attorney Aimee Hector acknowledged with hindsight that the arguments could have been handled differently, but said Jackson's comments were in response to defense arguments that jurors should have the courage to acquit.

"This rebuttal did not cross the line," she said.

The employees are serving prison terms ranging from 10 years for Bonventre; six years for Crupi and Bongiorno; and 2-1/2 years for O'Hara and Perez.