(Radio Iowa) — A central Iowa man will serve time in prison for mailing a threatening letter to a local teacher. Sixty-seven-year-old Mondell Olson was sentenced 18 months in prison after he admitted to sending a letter to a Nevada school teacher which contained a white powdery substance inside and a note indicating the substance was anthrax. Tests determined the power was not toxic. Olson had previously been convicted on harassment charges in Story County for leaving threatening voice mails to the Nevada High School and a student.