Baby Andrew case: US woman charged over death of baby abandoned in South Dakota ditch 38 years ago

A US woman has been charged over the death of a newborn baby who was abandoned in a ditch 38 years ago.

Police in South Dakota said they used DNA and genealogy sites to determine Theresa Rose Bentaas was the baby’s mother.

Bentaas was arrested and charged with murder and manslaughter over the 1981 death of the boy, known as Baby Andrew.

Bentaas told authorities last month that she had hidden her pregnancy from her friends and family and gave birth while alone in her apartment, according to a court document.

Bentaas allegedly said she then drove the baby to the area he was later discovered, a cornfield ditch in Sioux Falls.

Bentaas, now 57, said she was "young and stupid" and felt sad and scared as she drove away, according to the document. The baby died of exposure.

Bentaas, who was 19 when her son died, later married the infant’s father and has two living adult children with him, it was reported.

The case has gripped Sioux Falls for decades.

Roughly 50 people attended the child’s funeral, held more than a week after he was discovered.

Children left stuffed animals and a badge on his pyjamas read: "You are loved."

How did police gain the DNA in the case?

Retired detective Mike Webb said authorities used DNA from the baby exhumed 10 years ago and DNA obtained from Bentaas through a search warrant.

"I couldn’t be more pleased with the results today and the arrest and the closure that we find, as well as the hard work and dedication for the pursuit of justice for Andrew," police chief Matt Burns said.

Public genealogy databases have been used in other recent cases, including the capture last April of the suspected Golden State Killer in northern California and the arrest of a businessman accused of fatally stabbing a Minneapolis woman in 1993.

In South Dakota, authorities submitted a DNA sample from Baby Andrew to Parabon NanoLabs, which found two possible matches using a public genealogical database.

Police constructed a family tree and performed a “trash pull” to collect beer and water containers and cigarette butts at Bentaas’s home.

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