The Office of the State Medical Examiner says an Oklahoma man convicted of murder in the 1997 disappearance of his 8-year-old neighbor was strangled to death in his prison cell.

A report released Tuesday says 59-year-old Anthony Palma died from “ligature strangulation and blunt force trauma to the head” on Jan. 11 in his cell at the Oklahoma State Penitentiary in McAlester.

Palma was sentenced to life in prison for the presumed death of Kirsten Hatfield. The girl was kidnapped from her home in the Oklahoma City suburb of Midwest City and her body was never found.