LINCOLN, Neb. -- A 53-year-old inmate in the Nebraska State Penitentiary has died, according to NDCS.

Melvin Stamper died Sunday evening at the Nebraska State Penitentiary.

His sentence began on November 18, 2005, and he was serving an 18 to 34-year sentence for two counts of robbery and possession of a deadly weapon by a felon.

The charges originated out of Buffalo and Lincoln County.

The cause of death has not yet been determined and the Nebraska Department of Correctional Services says a grand jury will conduct an investigation, as is the case in all in-custody deaths.