A Long Island restaurateur who was a key witness in a public corruption investigation was sentenced to four years in prison Wednesday, ending an episode that churned up allegations of endemic wrongdoing that stretched across New York City and one of its most populous suburban areas. He testified for 17 days in two trials against Mr. Mangano, who is now serving 12 years in prison. On Wednesday, Judge Joan M. Azrack of the Eastern District of New York called Mr. Singh “a master of pay to play.” But she credited his help to prosecutors, which revealed a dark nexus of politics and business. “The extent and nature of his cooperation is possibly unmatched by any defendant in a corruption investigation,” Judge Azrack said. She also noted Mr. Singh’s age and health problems, as well as the support of his family, commending him for raising three successful sons.

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Persons: Harendra Singh, Edward P, Mangano, Joan M, Singh “, ” Judge Azrack, Ruby Organizations: of Locations: New York City, Nassau County, Eastern, of New York