After more than five grueling months, the trial of five ex-Madoff employees is nearing its conclusion.

The case of Dan Bonventre, Joann Crupi, Annette Bongiorno, George Perez and Jerome O'Hara is expected to go to jury on Monday at a federal district court in New York. They're accused of helping Bernard Madoff steal $20 billion from thousands of investors with his long-running Ponzi scheme. The charges they face include conspiracy to commit securities fraud.

All the defendants have pleaded not guilty. They say they didn't know that Madoff's firm was a front for a pyramid-style scheme, despite working there for many years.

Prosecutor Randall Jackson slammed that claim on Thursday, saying the defendants were willing participants in Madoff's fraud. He dismissed the notion that the employees knew nothing about the malfeasance as "an absurdity."

Jackson drew a comparison between the willingness of Madoff employees to turn a blind eye to the fraud and children pretending to believe in Santa Claus.

"Even after kids realize there's no such thing as flying reindeer, some act like they still believe," said Jackson, "because they like getting all those presents."

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But in closing arguments, Dan Bonventre's defense attorney Andrew Frisch reminded the jurors that while they're looking at the Ponzi scheme with the benefit of hindsight, Madoff employees couldn't.

"You wonder, if you had lived in Madoff's world, if you would have seen it," Frisch said. "So many people were taken in by the toxic cocktail of Bernie Madoff's stature on Wall Street."

Bonventre spent 40 years working for Madoff, and testified last month that he was as fooled by Madoff as any of the victims. He said Madoff went to great lengths to maintain his image as a magnanimous Wall Street wizard who cared about his employees.

"None of that was real," Bonventre testified. "Now I think [Madoff] was a terribly ill man. It's difficult to reconcile everything I knew about him for 40 years with everything I know now."

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Another former employee, Annette Bongiorno, testified that she spent years recording trades for Madoff that didn't exist, without truly understanding what she was doing.

"He told me what to do," she said. "I typed."

Federal prosecutors have spent years picking apart the claim Madoff made during his 2009 guilty plea that he acted alone.

Another former Madoff colleague, Frank DiPascali, Jr., served as a star witness for the government and provided details about the fraudulent firm's machinations.

DiPascali pleaded guilty to fraud and admitted to cooking the books during his 33 years at Madoff's firm.

"We were lying," DiPascali said on the stand. "I'm talking about trades that ... actually didn't exist."

But defense attorney Frisch dismissed DiPascali as a "pathological liar" and therefore unreliable on the stand, since his prime motive is to win a reduction in his prison sentence.

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DiPascali has yet to be sentenced.

Madoff was sentenced to 150 years and he is currently incarcerated in a federal prison in North Carolina. He is scheduled for release in 2139.