A South Dakota woman charged with murder in the death of her newborn who was abandoned in a ditch 38 years ago has been released from jail.

Theresa Bentaas, 57, has been in the Minnehaha County Jail since her arrest March 8. Investigators said they used advances in DNA evidence and genealogy sites to determine she was the mother of the infant, called Baby Andrew, whose body was found wrapped in a blanket in a cornfield ditch in Sioux Falls in February 1981.

Bentaas was released Monday, according to the Argus Leader , after a judge changed a $250,000 cash-only bond to a surety bond, which allows a defendant to work with a bail bondsman to be released while their case is pending.

Bentaas, who is charged with first- and second-degree murder and first-degree manslaughter, told authorities that she hid her pregnancy from her friends and family and gave birth while alone in her apartment, according to a court affidavit. Bentaas told authorities she then drove the baby to the area where he was later discovered.

The baby died of exposure.

Bentaas, who was 19 at the time, said she was "young and stupid" and felt sad and scared as she drove away, according to the document. She later married the infant's father and has two living adult children with him. The father won't be charged because he wasn't involved, authorities have said.

Retired Detective Mike Webb said authorities used DNA from the baby exhumed 10 years ago and DNA obtained from Bentaas through a search warrant. Authorities submitted a DNA sample from Baby Andrew to Parabon NanoLabs, which found two possible matches using the public genealogical database GEDmatch. Police constructed a family tree and performed a "trash pull" to collect beer, water bottles and cigarette butts at Bentaas' home.

Results from a cheek swab sample show there's "extremely strong evidence" to support a biological relationship between Bentaas and the child, according to the affidavit.

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Information from: Argus Leader, http://www.argusleader.com