LINCOLN, Neb. (AP) — A man convicted of sexual assault on children in two Nebraska Panhandle counties has died while serving a prison sentence of 40 to 60 years.

The Nebraska Department of Correctional Services says 77-year-old Larry Holladay died late last month at the Nebraska State Penitentiary in Lincoln. The cause of his death hasn’t yet been determined, but he’d been treated for a long-term medical problem.

State law requires a grand jury investigation any time a person dies in custody or while being arrested.

The department says Holladay was convicted of sexual assault and sexual assault on a child in Box Butte and Sheridan counties. He’d been imprisoned since January 2006.