A US man who spent more than 21 years on death row is free after a judge dismissed the murder charge against him over the 1988 stabbing death of a man found dead in a Cleveland park.

A county judge dismissed the charge of aggravated murder against Michael Keenan, 62, after determining evidence that could have exonerated him was withheld from his lawyers.

Keenan’s lawyer, John Hildebrand, said his client was “obviously thrilled” with the ruling.

“It’s unfortunate that he had to spend that time on death row,” Hildebrand said. “A lot of money was spent to keep him there because prosecutors concealed evidence.”

Richard Bell, the assistant prosecutor who handled the latest proceedings in the case, said in a statement that the prosecution will appeal. Bell said Keenan could have received a fair trial.

“We were prepared to prove for the third time that Keenan and his employees murdered Tony Klann,” Bell said.

Keenan was convicted twice of killing Tony Klann, 19. His first conviction was overturned after the Ohio Supreme Court determined prosecutorial misconduct, but he was convicted again in 1994, Hildebrand said.

Another man, Joe D’Ambrosio, also had been convicted of murdering Klann, but a Catholic priest who had befriended D’Ambrosio found evidence that could have helped both men at trial. The withheld evidence included police statements concluding that Klann could not have been murdered where prosecution witness Edward Espinoza, claimed the killing occurred, Hildebrand said.

Espinoza, who pleaded guilty to a reduced charge of manslaughter in the case and testified against Keenan and D’Ambrosio, was released in 2001 after serving 12 years in prison. He has since died.

D’Ambrosio was freed in 2010 by a judge who determined evidence that could have exonerated D’Ambrosio was withheld from his trial lawyers. Keenan continued his appeal, and a federal judge in April ruled that Keenan must be retried within 180 days or the verdict set aside.

Hildebrand said Keenan is considering suing the state for wrongful imprisonment.