An 86-year-old inmate who was convicted of murder in the death of his friend died Sunday morning at the Mountain View Correctional Facility.

Robert Craig of Clearwater, Florida died at the Charleston facility at about 6:45 a.m.

The Portland Press Herald reports that Craig’s death was attended by medical personnel.

In 2017, Craig was sentenced to 33 years behind bars for killing 86-year-old Leo Corriveau of Presque Isle.

An autopsy determined that Corriveau had been strangled, and suffered broken ribs and cuts on his arm and head.

Craig testified that he killed his friend in self-defense after the two got into an argument and fought outside the victim’s home.

The cause of the inmate’s death has not been released.