SIOUX FALLS, S.D. — A South Dakota judge on Thursday sentenced a woman to 10 years in the state prison system for her infant son’s 1981 death that went unsolved for decades.

Judge Bradley Zell called the sentencing of 60-year-old Theresa Bentaas a difficult decision that he belabored for weeks, in part because it was not clear whether her son died from complications during birth or abandonment in the South Dakota cold.

Zell was suspended nine years of the sentence, meaning Bentaas will likely spend two months in state prison and serve the rest of her time under community supervision.

The infant’s death was uncovered by the curiosity of two men, who were test driving a car in 1981 when they spotted blankets in a ditch.

An autopsy determined that the infant likely died from failure to assist in maintaining an airway during his birth and exposure.