A man convicted of murdering an eight-year-old girl was allegedly killed by his cellmate at the Oklahoma State Penitentiary.

According to The Oklahoman, a corrections officer discovered the body of Anthony Joseph Palma, 59, around 7.30pm on Friday during a regularly scheduled security check.

Reports say medical staff's efforts to revive Palma were unsuccessful and he was pronounced dead at 8.55pm.

Details on how Palma died were not released nor was the name of the inmate, but he was also serving time for first-degree murder, reported the newspaper.

Anthony Joseph Palma, 59 (left), was found in his cell around 7.30pm on Friday at the Oklahoma State Penitentiary. He was serving life in prison without parole for the 1997 murder of eight-year-old Kirsten Hatfield (right) in Midwest City, Oklahoma

Reports say medical staff's efforts to revive Palma (pictured) were unsuccessful and he was pronounced dead at 8.55pm. He's believed to have been killed by his cellmate, also serving time for first-degree murder

Palma died 13 months after he was sentenced to life in prison without parole for the murder of Kirsten Hatfield.

According to The Charley Project, Kirsten disappeared in May 1997. She was last seen at her home on the 1100 block of Jet Drive in Midwest City, Oklahoma.

Her mother, Shannon Hazen, said she put her daughter to bed around 11.30am and, when she checked in again between 6am and 6.30am, Kirsten was missing.

Blood was discovered on the bedroom windowsill and Kirsten's underwear was found in the backyard.

Her body has never been found.

Prosecutors say Palma, who lived two doors down from the home, abducted and sexually assaulted Kirsten before murdering her, reported The Oklahoman.

In October 2015, Palma was arrested after new testing found his DNA on Kirsten's bedroom windowsill and on her underwear.

The Charley Project says Palma knew Kirsten because, at the time of her death, he was dating her older sister.

Kirsten (left) disappeared from her home in May 1997. Blood was discovered on the bedroom windowsill and Kirsten's underwear was found in the backyard. New testing found Palma's (right) DNA on both the sill and her underwear

Palma lived two doors down from Kirsten and was still at the time of his arrest. He had maintained his innocence. Pictured: A search dog combs through the home and the yard of Palma after his arrest in October 2015

Palma insisted he was at home on the night of Kirsten's disappearance when he was questioned back in 1997 and in 2015, and had maintained his innocence.

One month after he was arrested, he unsuccessfully attempted suicide by slitting his wrists, news reports said.

This was not Palma's first run-in with the law.

His former landlady accused him of drugging and molesting her in 1982 in Walters, Oklahoma, reported News 9.

And in a case similar to Hatfield's, Palma allegedly assaulted a young girl in 1979 or 1980, also in Walters.

According to prosecutors, he sneaked into the girl's bedroom in the middle of the night. He was never charged.