LINCOLN, Neb. (AP) — Prison authorities say a 54-year-old inmate has died at a Lincoln hospital.

The Nebraska Correctional Services Department says Donald Krisor died around 4:15 a.m. Tuesday. The department says the cause of his death hasn’t yet been determined, but he was receiving treatment for complications related to a medical procedure. A grand jury will investigate because such is required whenever someone dies in custody or being arrested.

The department says Krisor had been assigned to the Tecumseh prison and had been serving a 30-year sentence for manslaughter and use of a deadly weapon in Douglas County.