NEW YORK (AP) -- A 1991 murder conviction was vacated on Friday after prosecutors told a New York City judge that the state's key witness had lied about who did it, a case linked to a retired detective at the center of dozens of wrongful conviction claims.

The decision at a hearing in Brooklyn cleared Derrick Hamilton, who had served 21 years in prison before being paroled in 2011.

"One day in prison is too much for an innocent man," Hamilton told reporters outside court. "It's exhilarating. It's a grateful day."

Derrick Hamilton, center, hugs his wife Nicole outside a courtroom after he was exonerated Friday. (AP Photo/Bebeto Matthews)
Derrick Hamilton, center, hugs his wife Nicole outside a courtroom after he was exonerated Friday. (AP Photo/Bebeto Matthews)
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At the hearing, prosecutor Mark Hale told a judge that a review of Hamilton's case concluded that a purported eyewitness to the fatal shooting was "unreliable, incredible and untruthful, and because of that Mr. Hamilton's due rights were violated."

Hamilton's defense team had claimed that Detective Louis Scarcella framed him by intimidating the witness into falsely identifying him as the shooter.

A finding last year in another case that Scarcella coached a witness to pick a suspect out of lineup has prompted a review of roughly 100 convictions, including about 70 that involved the former detective.

A special unit in the Brooklyn District attorney's office is doing the review, one of the nation's most ambitious efforts to determine whether old cases were handled properly. The unit has so far gotten 11 of them thrown out. Of those, four were investigated by Scarcella.

An attorney for Scarcella who attended the hearing had no immediate comment. The former detective has claimed he went by the book.

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