Corrections officials said an inmate at the Nebraska State Penitentiary died Monday. 

NDCS said in a statement that Amos Loyd, 57, died shortly before 5 p.m.  Loyd was 13 years into a 20- to 30-year sentence for robbery.

An official cause of death has not been determined. NDCS said Loyd was being treated for an undisclosed medical condition. 

A grand jury will conduct an investigation into the death.