The last defendant in the Bernard Madoff Ponzi scheme is going to jail three years after he pleaded guilty to helping conceal the massive fraud from regulators.

Irwin Lipkin, 77, will spend six months in prison for his role in the scheme that defrauded investors of billions of dollars in investments.

Lipkin is the last of 15 people convicted in the scam, in which Madoff promised, and appeared on paper to deliver, unrealistic returns on investments. "The roughly $17.5 billion in principal invested by retirees, charities and other clients over decades was mostly gone — paid out as fake profits or raided by Madoff's family and cronies," according to The Associated Press.

Madoff was arrested in December 2008 just as the Great Recession was gaining steam after tips to law enforcement from his sons, Andrew and Mark Madoff, who worked in their father's firm have denied being directly involved in the scheme. Andrew died last year of cancer at age 48. The senior Madoff was sentenced to 150 years in prison.

Lawyers for Lipkin argued that he should not be imprisoned on account of his frail health, but prosecutor David Abramowicz said it was important to remember that Madoff "didn't do this alone."

The AP reports:

"A frail-looking Lipkin, who was hired as one of Madoff's first employees in the 1960s, had admitted in his guilty plea that he knowingly certified false documents. But he also told U.S. District Judge Laura Taylor Swain that during the decades he worked for Madoff, he believed the operation 'was absolutely on the up and up.'"

"Still, he added: 'I would like to apologize to the court and to everybody else who may have been hurt by the things that I've done.' "

Last year, five former employees of Madoff's firm were also found guilty of conspiracy and securities fraud for helping carry out the elaborate scheme.

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