The accountant in Bernard L. Madoff's giant Ponzi scheme, David G. Friehling, received a relatively light sentence of home detention but no additional prison time Thursday because of his cooperation with prosecutors.

In Federal District Court in Manhattan, Judge Laura Taylor Swain sentenced Mr. Friehling, 55 years old, to two years of supervised release, one of those in home detention, and several hundred hours of community service.

She cited his extensive cooperation with prosecutors in unraveling Mr. Madoff's decadeslong fraud.

Mr. Friehling, who had been the outside auditor for Mr. Madoff's securities firm and handled the personal tax accounting for Mr. Madoff and his sons, pleaded guilty in 2009 to nine criminal counts, including securities fraud, investment-adviser fraud and violations of tax laws.

Mr. Madoff, whose scheme cost about $17.5 billion in losses for customers around the world, is serving a 150-year sentence in federal prison.

In the unlikely cast of characters behind the largest Ponzi scheme ever uncovered—a number of Mr. Madoff's closest confederates in his firm had no college degree and little to no financial experience before joining his firm— Mr. Friehling fit in well.

Mr. Friehling had inherited the Madoff account from his father-in-law, Jerome Horowitz, who had worked for Mr. Madoff for decades, and he worked out of a storefront office as a sole practitioner in New York state. According to court documents, he barely reviewed the Madoff Securities reports and documents he received and didn't verify the information on assets, bank accounts or earnings.

Randall Jackson, an assistant U.S. attorney, said in a sentencing memo to the court that "Friehling's criminal abdication of his auditing duties was one of the biggest contributors to the perpetuation of the Madoff Ponzi scheme."

Mr. Jackson added, "But for Friehling's rubber stamping of Madoff Securities, it is almost certain that the fraud could not have continued for nearly as long as it did."

But, Mr. Jackson said, "Friehling has been a model witness and cooperating defendant" and he provided "exceptional testimony" in trials of Mr. Madoff's staff. "Friehling is that rare defendant who has experienced deep and true remorse for his actions and their impact on others," he wrote.

Mr. Jackson also noted Mr. Friehling's contention that he was unaware of the fraud because he hadn't reviewed the firm's documents.

Write to James Sterngold at james.sterngold@wsj.com

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