A DNA test has revealed that a man who was found not guilty in the rape and murder of a horse groomer at a Florida racetrack more than 30 years ago was, in fact, the killer, the authorities said on Wednesday.

Lawyers for the man, Robert Earl Hayes, had asked investigators in 2020 to retest the strands of hair found in the hand of the horse groomer, Pamela Albertson, after she was raped and killed in February 1990 at the Pompano Beach racetrack in South Florida, where they both worked. The lawyers believed that the findings would help exonerate their client in the 1987 killing of another racetrack worker in Oneida County, N.Y., for which Mr. Hayes is currently in prison, the New York Times reports.

In the New York case, Mr. Hayes pleaded guilty to manslaughter, arson and burglary in 2004. He was sentenced to 15 to 45 years in prison and is eligible for parole in 2025.

But investigators also retested vaginal DNA collected from Ms. Albertson, and found that it was a match with Mr. Hayes, effectively proving that he was guilty all along, said Harold F. Pryor, the Broward County state attorney in Florida.

Mr. Pryor cannot retry Mr. Hayes, now 58, in the Florida case because the Constitution prohibits people from being retried for substantially the same crime if they were already acquitted. But Mr. Pryor is asking the parole board in New York to keep Mr. Hayes in custody.