NEW YORK — Imprisoned financier Bernard Madoff’s claim that he carried out a nearly $20 billion fraud by himself has been firmly rejected by a jury that convicted five of his former top employees of all charges that they aided his crimes.

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

For more than five months, jurors listened to dozens of witnesses and saw hundreds of exhibits before convicting Madoff’s former secretary, his director of operations, an account manager and two computer programmers of multiple charges.

“The evidence was just overwhelming,” juror Craig Parise told reporters. As promised by prosecutors at the trial’s start last October, evidence showed investors big and small were swindled, from Florida retirees to celebrities such as 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 Daniel 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.