PORTLAND — An inmate at the Maine State Prison in Warren serving a murder sentence died at a Portland hospital early Wednesday, according to Maine Department of Corrections spokesman Scott Fish.

Paul Henry Gray, 68, formerly of Houlton, died at approximately 5:30 a.m. at Maine Medical Center. He had served approximately 21 years of a 55-year sentence for murder, Fish said. No further details about his death were released.

Gray killed Betty Curliss in October 1992 following an argument, according to Bangor Daily News archives. Gray and Curliss were sharing an apartment in Houlton.

At the time of his arrest, Gray told police the couple had argued about money the night before Curliss died. In anger, he said, he ripped off Curliss’ clothes and forced her onto the bed, putting his hands on her shoulders. He said he did not recall what happened after that.

Gray found Curliss dead the next morning and called police. Investigators determined she had been strangled with an electrical cord and some of her ribs had been broken.

A jury of seven women and five men returned a guilty verdict against Gray in September 1993 in just 42 minutes.

Gray had been handed down his sentence in October 1993, Fish said. His scheduled release date was Jan. 4, 2028.

Maine State Police and the medical examiner were notified of Gray’s death on Wednesday by the Attorney General’s Office, which is protocol for such cases, and both are investigating.