Almost four decades after the body of a baby boy was found in a ditch in South Dakota, police have tracked down his mother.

Theresa Rose Bentaas, 57, was arrested last Friday and charged with the murder of the little boy who authorities named 'Baby Andrew'. The baby's body was found in a ditch in a cornfield in the city of Sioux Falls in February of 1981. He was alive when he was placed there, reports the The Atlantic, but passed away after being exposed to severe weather conditions. The case gripped the local area but as time went on, hope dwindled that answers would be found. Then, forensic genealogy came along. Police used DNA from the body of baby Andrew, which was exhumed ten years ago. Using genealogy websites, they were able to trace relatives of the baby. They eventually tracked down Ms Bentaas and matched her to the baby's DNA, proving she was his mother. Ms Bentaas admitted to abandoning him when she was 19, telling police she was "young and stupid". She had concealed the pregnancy from her family and gave birth to him while alone in her apartment. She then drove to the field and left him there. Police also identified the father of the baby - the man who Ms Bentaas is now married to. They established that he did not know about the pregnancy at the time and was unaware of what his wife had done. Ms Bentaas had seen news reports after the baby's body was found but said she was "in denial that she was the one responsible for that." She was charged with murder in the first degree, murder in the second degree and manslaughter in the second degree.