An Oklahoma prison inmate took justice into his own hands last month — beating and strangling a convicted child killer to death inside the cell they shared, according to officials.

Anthony Palma, 59, was allegedly murdered by his cellmate, Raymond Pillado, on Jan. 11 at the Oklahoma State Penitentiary in McAlester.

A medical examiner’s report, which was obtained Wednesday by KFOR, described the cause of death as “ligature strangulation and blunt force trauma to the head.”

Palma had been sentenced to life in prison two years ago for a 1997 cold-case murder involving an 8-year-old girl whose body was never found. Pillado, 35, is also serving several life sentences for murder and shooting with intent to kill, among other charges.

Palma’s death was reported last month, but the cause was not initially known. Department of Corrections officials at the time said they believed he was ultimately killed due to the nature of his crime.

“Those who are serving time for victimizing children, they are definitely more vulnerable,” explained DOC spokesman Matt Elliott.

The girl whom Palma was convicted of killing, Kirsten Hatfield, lived just two doors down from him at the time of her disappearance and presumed death, according to reports.

DNA testing eventually linked Palma to the crime and he was found guilty of kidnapping Hatfield, sexually assaulting her and killing her.

Authorities told KFOR back in January that they were planning on interviewing Palma later this year in hopes of finally learning the location of Kirsten’s remains.

“We’ve not had closure on this case and we may never have closure because we wanted to find her body and bring her home,” said Midwest City Police Chief Brandon Clabes. “Our hopes are, with any case like this, the suspect who’s convicted … in this case, it was Anthony Palma … that hopefully he would have some inkling of a conscience, maybe intervention by a higher power, maybe God, and come out and tell us exactly what he did with her.”

Kirsten’s mother, Shabnon Hazen, doesn’t plan to “give up hope” just yet.

“I’m not going to … I’m just not,” she told reporters last month. “I don’t have to at this point.”

With Post wires