LINCOLN, Neb. (AP) – Nebraska prison officials say a 64-year-old inmate at the Nebraska State Penitentiary in Lincoln has died. The Nebraska Department of Correctional Services said in a news release that Mark Nielson died Friday afternoon at a Lincoln hospital. The release says his cause of death has not yet been determined, but noted that Nielson was being treated for a medical condition. The department did not say what ailment afflicted Nielson, who began serving an 8- to 10-year sentence for methamphetamine trafficking in 2016. State law requires a grand jury investigation anytime someone dies in state custody.