BEACON, N.Y. - The man convicted in the 1975 killing of a Nassau County police officer has been found dead in prison, officials say.

John MacKenzie was pronounced dead Thursday morning at Fishkill Correctional Facility in Beacon, New York, located in Dutchess County, according to state corrections officials.

As News 12 has reported, MacKenzie shot Nassau Police Officer Matthew Giglio more than 40 years ago. The officer was responding to a report of a burglary in West Hempstead when he was shot, and he slipped into a coma and died a few weeks later.

MacKenzie was convicted in Giglio's death and was sentenced to 25 years to life in prison. He had served 40 years behind bars, but became eligible for parole every two years. Giglio's family fought to keep MacKenzie behind bars.

His death comes just weeks after he was denied parole for the ninth time.

It is unclear at this time how MacKenzie died. News 12 is told that MacKenzie's official cause of death will be determined by the Nassau County Medical Examiner’s Office.

In a 2000 interview with News 12, MacKenzie said he was remorseful, but said he didn't remember the shooting because of drug use. "After years of reading everything, I came to the realization that I did, and that was a hard pill to swallow," MacKenzie said at the time.

News 12 spoke to Giglio's children earlier this summer, when MacKenzie was up for parole again.

"It took MacKenzie seconds to pull the trigger that night, but it caused my family decades of pain and suffering," the officer's daughter, Regina Giglio, said at the time.

Officer Giglio worked in the 5th Precinct in Elmont. A plaza along Corona Avenue is now dedicated to his memory.