An Akron man has pleaded not guilty to a charge that he killed his mother. 44 year-old Jonathan Neunaber made his plea to the murder charge on Wednesday in Plymouth County District Court in Le Mars. County Attorney Darin Raymond has said Neunaber admitted to causing the death of 80-year-old Esther Grace Neunaber. Her body was found July 9 at her Akron home with the body of her 83-year-old husband, Donald. The cause of Donald Neunaber's death has yet to be determined. Authorities have said the couple died violently.