The leader of the main Nassau County police union called on the state Parole Board Friday to deny the release of the man convicted of killing Officer Matthew Giglio in 1975.

"We're here today to ask the public's support to make sure the killer of Matthew Giglio is denied parole and remains in jail," said James Carver, president of the Nassau County Police Benevolent Association.

"Unfortunately, the system allows him to be up for parole every two years, and this is something the family has to go through," Carver said at union headquarters in Mineola.

Doreen Giglio-Velardi, a New Jersey resident and daughter of the slain officer, praised the union for its efforts. "They're our alarm clocks, every two years," she said.

In October 1975, John MacKenzie, then 29, shot and fatally wounded Giglio, 35. MacKenzie, formerly of Whitestone, Queens, has been seeking parole since 2000, when he served the minimum 25 years required by his life sentence.

Giglio was investigating a store burglary in West Hempstead when MacKenzie exited the store and fired a single shot into Giglio's chest. The officer, who had three young children, died weeks later.

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When the Parole Board last denied MacKenzie's request for release in 2012, it said in a brief decision that he had killed a police officer and had a "larcenous" history, and cited "significant community opposition."

Carver Friday urged people to write letters, urging the board to again deny MacKenzie parole. He is expected to appear before the board in mid-June, according to a spokeswoman for the state Department of Corrections and Community Supervision.

Nassau County District Attorney Kathleen Rice Friday released a letter she wrote to the Parole Board last month in which she said MacKenzie had at various times claimed he was innocent or insane, before finally expressing remorse.

"That remorse . . . has no more credibility than any of his earlier claims," she wrote."Moreover, no amount of remorse can reverse the damage caused by MacKenzie's actions, or change the fact that he deserves to spend the rest of his life in prison."