A former controller at Bernie Madoff's investment firm was sentenced to 6 months in prison in Manhattan federal court Wednesday, officially closing the door on criminal prosecutions stemming from the massive Ponzi scheme.

Irwin Lipkin, 77, of Paramus, New Jersey, was the first nonfamily member hired by Madoff when he opened his securities business in the 1960s. He pleaded guilty in 2012 to conspiracy and falsifying records to help keep the $17 billion fraud from being detected.

He was the last of 15 defendants, including Madoff, to be sentenced for crimes related to the fraud. Manhattan U.S. Attorney Preet Bharara called the end of his case "the close of another chapter in this tragic tale of unchecked greed."

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Lipkin, appearing frail, asked U.S. District Judge Laura Taylor Swain for no jail time. He insisted, like other ex-employees who were prosecuted, that while he broke the law and cut corners he never knew Madoff's entire operation was a fraud.

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

Madoff is serving a 150-year prison term. His brother Peter received a 10-year sentence. Five employees who went to trial and were convicted received sentences from 2 1/2 years to 10 years.

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But several Madoff employees who cooperated with the government received probation. Lipkin, who did not cooperate, will be required to serve 18 months of house arrest after his incarceration is over.

Prosecutors said that despite Lipkin's age and health issues, he needed to do prison time because his support was critical to Madoff.

"He didn't do it alone because he couldn't do it alone," prosecutor David Abramowicz told the judge about Madoff. "He needed the help of people like Mr. Lipkin." With AP