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For four decades, Keith Bush insisted he had been convicted as a teenager of a murder he did not commit: strangling a 14-year-old girl in Bellport, N.Y. The police, he said, had beaten him and forced him to sign a confession that he had never read.

While imprisoned, he had enlisted the help of a lawyer at Pace Law School, who sued to obtain records and unearthed evidence showing Mr. Bush had not gotten a fair trial. Even after he was released from state prison on parole, Mr. Bush continued to fight to clear his name.

On Wednesday morning, 44 years after his arrest, Mr. Bush was exonerated in Suffolk County District Court in Riverhead, Long Island. The Suffolk County district attorney, Timothy D. Sini, asked a judge to throw out the conviction, saying prosecutors never told the defense the police had interviewed another possible culprit.

“I cannot give you that which was taken from you in the 1970s, but what I can restore to you today is your presumption of innocence,” Judge Anthony Senft Jr. told Mr. Bush.