A federal jury in New York on Monday found five former employees of Bernard Madoff guilty of helping the jailed scammer pull off one of the longest and largest investment frauds in history.

The 12-person jury dismissed the employees’ claims that they had been duped by Madoff, in some cases working for decades without a clue that their boss was running a giant Ponzi scheme.

The five defendants are back-office manager Daniel Bonventre; portfolio managers Annette  Bongiorno and Joann Crupi; and computer programmers Jerome O'Hara and George Perez. They were convicted of conspiracy to defraud investors and securities fraud.

Each faces decades in prison for enabling the fraud by conducting the daily mundane back office work that made it appear to Madoff’s clients, as well as regulators, that Madoff was conducting legitimate trades in an effort achieve profits.

“As the jury unanimously found, these five defendants played crucial roles in constructing and maintaining the house of cards that was the Madoff investment fraud,” U.S. Attorney for the Southern District of New York Preet Bharara said in a statement following the verdict.

The case was the first criminal trial to spring directly from Madoff’s scheme, which investigators  say operated for more than two decades and bilked investors of an estimated $17 billion.

According to an indictment handed down against the five defendants in July, the employees assisted Madoff by, among other activities, creating false documents that were distributed as statements to Madoff’s investors. The statements used complicated Wall Street jargon to suggest Madoff was employing sophisticated techniques to generate the handsome profits he used as his calling card.

Since Madoff’s arrest, investigators have revealed that he made virtually no trades at all and fabricated all his records. He used the money generated from new investors to cover profits paid to older investors – a classic Ponzi scheme.

Madoff turned himself in in late 2008 as the fraud was unraveling, undone by the onset of the financial crisis. The scheme collapsed as many of his clients sought redemptions and Madoff realized he couldn’t possibly repay all those who wanted their money back.

The trial of the five Madoff staffers -- their cases were tried simultaneously -- lasted over five months and closing arguments alone lasted more than 25 hours and stretched over two weeks. More than 40 witnesses were called to testify and some 1,600 exhibits introduced.

All five offered slightly different versions of the same defense -- Madoff was the only person in the office who knew the whole story. Everyone else performed their specific functions without realizing they were contributing to a massive financial fraud.

But Madoff’s right hand man, Frank DiPascali Jr., the long-time office manager of Bernard L. Madoff  Securities, cast doubt on that defense as a witness for the prosecution.

DiPascali pleaded guilty in 2009 to multiple counts of fraud and was a key witness for the prosecution during the trial. In effect, he told the jurors that everyone in the office knew Madoff was running a scam.

Jury deliberations lasted four days.

With the convictions, 14 former Madoff employees, including Bernard Madoff’s brother Peter, have now pleaded guilty or been found guilty by a jury of helping Madoff operate the fraud.

Madoff has claimed some of the big banks where he held accounts knew what he was doing, but he has never pointed the finger at anyone in his office.

“These convictions, along with the prior guilty pleas of nine other defendants, demonstrate what we have believed from the earliest stages of the investigation: this largest-ever Ponzi scheme could not have been the work of one person,” said Bharara.

Madoff pled guilty to a slew of offenses in June 2009 and is serving a 150-year sentence in federal prison.

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