Imprisoned financier Bernard Madoff's claim that he carried out a nearly $20 billion fraud by himself was firmly rejected by a jury Monday, when it convicted five of his former employees of participating in his crimes.

Among those convicted were two computer programmers: George Perez, a 48-year-old from East Brunswick, N.J. who was first hired by Bernard L. Madoff Investment Securities in 1991, and Jerome O'Hara, 51. The two were found guilty of having developed a software program that automated fake securities transactions to fool investors and investigators. The program generated "information out of thin air," as one prosecutor put it.

Director of operations Daniel Bonventre, 67, Madoff secretary Annette Bongiorno, 66, and account manager JoAnn Crupi, 53, were also found guilty of playing a knowing part in Madoff's fraud.

The verdict means that more than a dozen people have either pleaded guilty or been convicted of charges related to the mammoth fraud Madoff engineered for decades before the economy's 2008 collapse exposed it for the Ponzi scheme it was.

Guilty verdicts were returned on charges of conspiracy to defraud clients, securities fraud and falsifying the books and records of a broker dealer, among others. Maximum potential sentences range from 78 years to 220 years in prison, but the actual sentences are likely to be far less. Sentencing hearings were scheduled for late July.

U.S. Attorney Preet Bharara said the convictions, along with the previous guilty pleas of Madoff and eight other defendants, demonstrate what prosecutors have believed since the early stages of the investigation: "This largest-ever Ponzi scheme could not have been the work of one person."

"These defendants each played an important role in carrying out the charade, propping it up and concealing it from regulators, auditors, taxing authorities, lenders and investors," Bharara said.

For more than five months, jurors listened to dozens of witnesses and saw hundreds of exhibits before convicting the five defendants. 

"The evidence was just overwhelming," juror Craig Parise told reporters as he left the courthouse. As promised by prosecutors at the trial's start, evidence showed investors big and small were swindled, from Florida retirees to celebrities such as movie director Steven Spielberg, actor Kevin Bacon and Hall of Fame pitcher Sandy Koufax. Even Nobel Peace Prize winner and Holocaust survivor Elie Wiesel was cheated.

"The list of Bernard Madoff's victims now includes these five former employees," said Andrew Frisch, attorney for Bonventre. Bonventre testified in his defense that he was manipulated by Madoff since 1968 just the same way his boss snookered the Securities and Exchange Commission and top financiers on Wall Street as he rose to be Nasdaq chairman.

Longtime Madoff secretary Bongiorno followed him to the witness stand, claiming she too was victimized by a boss who charmed her for four decades even as he kept secret how he managed to return double-digit growth in his clients' accounts year after year, in good times and bad.

She said Madoff told her they could make money in a down market by shorting stocks, and she believed him.

Parise said the testimony by Bongiorno and Bonventre "did not help their cause."

Another juror, Sheila Amata, said she hoped "this brings some level of closure" to the victims. She added that the "facts spoke for themselves" in the case and that Madoff, who is serving a 150-year prison sentence, "seemed to have a split personality." Evidence showed him showering employees, friends and some select customers with favors and riches while he plundered the investment accounts of others.

The trial, one of the longest in Manhattan federal court history, was the first to result from the massive fraud revealed in December 2008 when Madoff ran out of money during the nation's financial crisis and was arrested.

At a guilty plea three months later, Madoff insisted he acted alone before being led away to prison.

In the following months, prosecutors built their case against the five defendants. Since October, they've shown the jury the role each played in creating and mailing out tens of thousands of phony monthly statements and trading confirmations to make it look as if customers were making money in the market.

Madoff's thousands of victims included individuals, trusts, pension funds, hedge funds and nonprofit organizations. The scheme wiped out people's life savings, ruined charities and foundations, and apparently pushed at least two investors to commit suicide.

Clients lost nearly $20 billion. A court-appointed trustee has recovered much of the money by forcing those customers who received big payouts from Madoff to return them. When the fraud was revealed, Madoff admitted that the nearly $68 billion he claimed existed in accounts was only a few hundred million dollars.

As the verdict was read, the defendants largely took the convictions in stride except for Crupi, who looked shocked when the first guilty verdict was read and later shook her head.

U.S. district judge Laura Taylor Swain rejected requests that the defendants be immediately detained. The defendants hugged family members. They declined to comment as they walked past reporters.

Attorney Eric Breslin, representing Crupi, said, "The name Madoff was a tall mountain to climb. I think it's just a fact."

One case remains outstanding, that of a former senior tax partner at the accounting firm Konigsberg Wolf & Co. who was charged with aiding Madoff by directing others to falsify records to conceal his fraud.

The centerpiece of the prosecution's case in this trial was Frank DiPascali, Madoff's former finance chief, and five other insiders who pleaded guilty and agreed to cooperate. He and others spoke often about Madoff, "Bernie" as everyone called him, along with his relatives, including his brother, wife and two sons. One of the sons committed suicide two years after the fraud was revealed.

Defense lawyers in closing arguments insisted their clients were victims, too, losing tens of millions of dollars they had entrusted to their boss.

The verdict was delivered after the jury deliberated for about 20 hours over a period of two weeks. The panel was down to 11 jurors after one juror became sick during deliberations and was dismissed.

The defendants were described by prosecutors as "necessary players" in the fraud. They said Bongiorno, hired in 1968, and Crupi, hired in 1983, used old stock tables to fabricate account statements and other fake records that fooled the SEC. The government said they also enjoyed tens of millions of dollars in salaries and bonuses, including $2.5 million for a beach house for Crupi as the Ponzi scheme was falling apart.

Madoff, 75, is serving his sentence at a federal lockup in North Carolina.

Based on reporting by The Associated Press.

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