McAlester, OK – Anthony Palma was killed Friday in prison, just 13 months after he was convicted of killing an eight-year-old girl in 1997.

Kirsten Hatfield was eight years old in 1997 when she went missing, and her body has never been found, according to The Oklahoman.

Prosecutors said that Palma took Hatfield from her home to sexually assault her after she went to bed on May 13, 1997.

At the time, he lived two houses away from his victim, The Oklahoman reported.

Hatfield’s disappearance was considered a cold case until advanced DNA testing was conducted on evidence from the crime scene.

DNA tests showed that blood found on Hatfield’s underwear belonged to Palma.

The underwear was found in the backyard of her house, according to KFOR.

Blood was also found on the partially-opened window to Hatfield’s bedroom.

Palma denied any involvement in the little girl’s disappearance but police narrowed down DNA from at least 24 people to just him, KFOR reported.

He was working as a groundskeeper at Lake Thunderbird State Park, and still living in the same house, when he was arrested, according to The Oklahoman.

Palma was convicted and sentenced to life in prison without the chance for parole in 2017.

He did not appeal his conviction.

A corrections officer was doing a routine security check at about 7:30 p.m. on Jan. 11 and found the 59-year-old Palma unresponsive in his cell, according to The Oklahoman.

Medical staff tried to save him but were not successful. He was pronounced dead at 8:55 p.m.

The Oklahoma Corrections Department confirmed it was investigating the homicide at the Oklahoma State Penitentiary.

Investigators consider Palma’s cellmate as a suspect in the murder. His cellmate was also incarcerated for first degree murder, The Oklahoman reported.

Prison authorities have not released the name of Palma’s cellmate.