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A South Dakota mother was charged Thursday with murdering her newborn more than three decades after police said she left the baby in a ditch in the Sioux Falls area.

The baby was alive when Theresa Rose Bentaas, 57, left him on the side of a road in 1981, Sioux Falls Police Chief Matt Burns said during a news conference. The baby was found on by residents test driving a car in the area.

An autopsy revealed that the baby was born full-term, and "slowly succumbed to exposure," Burns said.

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"He had been loosely wrapped in a blood-stained blanket and left all alone in the cold," he said.

Theresa Rose Bentaas Minnehaha County jail

The baby was given the name Andrew by a local cemetery which offered to bury the newborn, according to authorities.

Authorities exhumed the baby's remains a few years ago to collect DNA samples but could not find matches, Det. Michael Webb said.

A few months ago, authorities worked with a DNA technology company and found several family trees that possibly connected the baby to residents in Sioux Falls. One of them was a match with a woman believed to be the child's grandmother.

During the investigation, detectives obtained a sample from Bentaas and on Monday confirmed she was the mother of the baby. Bentaas was a "young teenager" when she gave birth, authorities said.

Authorities were also able to find the baby's father, Webb said. Bentaas was interviewed by police last week and was arrested Friday. She is charged with first and second-degree murder and first-degree manslaughter.

Webb said the baby's father, whose name is not being released, was not arrested because he did not know about the pregnancy.