Five former aides to investment manager Bernard Madoff were convicted on Monday of charges that they helped their boss conceal his multibillion-dollar Ponzi scheme for years.

A federal jury in New York found back-office director Daniel Bonventre, portfolio managers Annette Bongiorno and Joann Crupi, and computer programmers Jerome O’Hara and George Perez guilty on all counts, including securities fraud and conspiracy to defraud clients.

The five-month trial was one of the longest white-collar criminal trials in Manhattan federal court history, featuring dozens of witnesses and thousands of documents. It is the first criminal trial stemming from Madoff’s fraud.

The five defendants will be sentenced in late July.

“The scheme these defendants helped perpetrate cost innumerable investors their life savings,” U.S. Attorney Preet Bharara said in a statement. “Now it likely will cost the defendants their freedom.”

Madoff, 75, is serving a 150-year-prison sentence after pleading guilty in March 2009 to running the Ponzi scheme, estimated to have cost investors more than $17 billion of principal. He was arrested in December 2008.

Nine other people have pleaded guilty in connection with Madoff’s fraud, some of whom testified at the trial as cooperating government witnesses.

As the jury foreman said “guilty” 59 times in a row, there was no visible reaction from the defendants, who each faced anywhere from eight to 20 charges.

“The list of Bernard Madoff’s victims now includes these five former employees,” Andrew Frisch, a lawyer for Bonventre, said after the verdict, adding that he plans to appeal.

There was little dispute that various defendants engaged in activities such as backdating fake trades and creating false documents. Instead, the case turned on whether they knew at the time that they were aiding Madoff’s fraud.

The defendants claimed Madoff duped them into becoming unwitting accomplices, using a potent combination of charm and deception.

“Why wouldn’t she believe him?” Roland Riopelle, the lawyer for Bongiorno, said during his closing argument. “He was the head of the firm and the chairman of NASDAQ. She was by design, by Mr. Madoff’s design, living in her own little bubble.”

But prosecutors pointed to internal documents seized from Madoff’s investment firm, including handwritten notes from the defendants, as clear evidence they knew what was happening.

“The notion that these defendants didn’t know the trading was fake is an absurdity,” Assistant U.S. Attorney Randall Jackson said at the end of the trial.

The key government witness was Madoff’s right-hand man, Frank DiPascali, who testified as part of a plea deal and implicated each of the five defendants in the fraud.

Defense lawyers urged the jury to disregard his claims, calling him an inveterate liar desperate to avoid a lifelong prison term. But several jurors interviewed after the verdict said they found DiPascali’s testimony credible.

“It was pretty captivating,” said Sheila Amato, an art teacher.

By contrast, jurors scoffed at the testimony of Bongiorno and Bonventre, who surprised trial observers by taking the stand in their own defense to deny knowing about any fraud.

Nancy Goldberg, an instructional assistant for at-risk public school students, said the testimony was “embarrassing.”

Riopelle said he did not regret putting Bongiorno on the stand, as it was the only way to show the jurors she “never understood the consequences of her actions.”

The government said Bonventre helped conceal the fraud by manipulating the firm’s general ledger. He also deceived regulators, auditors and bankers, filed false tax returns and helped Madoff evade taxes as well, prosecutors said.

Prosecutors accused Crupi and Bongiorno of backdating fake trades in customer accounts months, and sometimes years, after they purportedly occurred.

And O’Hara and Perez were accused of writing computer programs that generated fake trade records to fool auditors, prosecutors said.

The trial provided an intimate look at Madoff’s fraud and the intricate structure of lies that kept it afloat, with Madoff fooling even his most trusted aides into believing he had assets stashed somewhere.

No one at the firm knew the entire truth; even DiPascali, who was deeply involved in the fraud, said he didn’t realize it was a Ponzi scheme until Madoff confessed to him just days before his arrest that he had run out of money.

Asked whether the defense could have anything differently, Eric Breslin, a lawyer for Crupi, said, “Madoff was a tall mountain to climb.”

The case is U.S. v. O’Hara et al, U.S. District Court, Southern District of New York, No. 10-cr-00228.

(Reporting by Joseph Ax; Additional reporting by Nate Raymond and Jonathan Stempel; Editing by Dan Grebler, David Gregorio and Bernard Orr)