On Feb. 27, Theresa Rose Bentaas received a knock on her door.

She may not have anticipated who was paying her a visit, but the date's alleged significance for the South Dakota woman was a clue. Police came to Bentaas' house on the day they say her firstborn son would have turned 38. Prosecutors now say she is the reason he died as a newborn, citing new DNA evidence they said link her to the cold case.

Baby Andrew John Doe, as he came to be known, was found dead Feb. 28, 1981, after some Sioux Falls residents spotted what looked to be blankets covered in a red liquid in a local ditch.

That liquid turned out to be blood, and inside the blankets laid a newborn baby boy, officials said.

Tears had frozen on the tiny baby’s cheeks, Lee Litz, who discovered the boy, later told the Argus Leader.

“To see a child thrown away like that — how could someone do that?” Litz said.

He had been alive when he was abandoned outside, where officials said he “slowly succumbed to exposure.”

The coroner would determine the baby had been lying in the ditch for about 24 hours before being discovered.

He lived for roughly two hours before he froze, the coroner found. His umbilical cord had not been cut and the placenta was still attached, officials said.

The case left its mark on the community, local reports at the time showed. He was given a funeral, which was attended by about 50 people, and he was interred at St. Michael’s Cemetery. His casket was decorated with carnations and the pajamas he was laid to rest in were adorned with a pin that said “You are loved.”

His grave would be visited often, including by Litz, who would come to regard the child as his own. “I think about what he’d be doing today if he was around and would have had a chance,” Litz told KSFY.

But he wasn't Litz's; he wasn't anyone's, it seemed. His headstone bore the name that he would be known by, Andrew, but the moniker that followed — John Doe — would serve as a reminder for more than three decades that no one ever came forward to claim him as their own.

And without his family, there was little for police to go on to find who was responsible for Andrew’s death.

“The investigators worked very diligently during that time, however, they did not have anything that we have today, as far as DNA technology, and the advances that we have today,” Det. Michael Webb told reporters. “They ran out of leads very quickly … they simply got no tips at all that warranted anything that would point us to this family.”

Webb, an investigator with the Crimes Against Persons section of the Sioux Falls Police Department, took on the case in 2009 and worked it ever since. That year, Webb exhumed Baby Andrew’s body to extract DNA from his bones and tissue.

When the DNA profile didn’t have any matches in the South Dakota DNA database, Webb then turned to Parabon NanoLab, the DNA technology company whose breakthroughs in genetic analysis have helped law enforcement agencies make arrests and identify suspects in decades-old unsolved murders.

“No one’s going to [Parabon NanoLab] for small cases … these are cold cases, these are unidentified human remains that they’ve never been able to identify,” Webb said.

Parabon found possible genetic family matches that Webb’s team was able to use to create a family tree that led to Theresa Bentaas, 57, he said.

Police said they obtained a search warrant for Bentaas’ DNA, which came back a match to Baby Andrew’s. Her husband was found to be the baby’s biological father, but he was not charged in the case, Webb said. In interviews, police learned that the father did not know about his dead son.

Bentaas, whose maiden name was Josten, was charged with murder in the first degree, murder in the second degree and manslaughter in the second degree, Webb said. She's being held on a $250,000 bond.

Police said Bentaas told them she was “young and stupid” and kept the pregnancy a secret from family and friends, according to an affidavit obtained by the Argus Leader. She allegedly said she had the baby alone in her apartment before leaving him in a ditch and driving away, cops said.

Bentaas and her husband married more than five years after Baby Andrew’s birth. They now have two living adult children, according to reports.

She was not among the 50 people who attended Baby Andrew’s funeral, Webb said. Police said Bentaas told them she was "in denial," and that while she had seen the news coverage of the baby, she did not want to believe he was hers.

But that denial would come crashing down nearly 40 years later, when on Feb. 27, police commemorated what should have been Baby Andrew’s 38th birthday by knocking on his mother's door, they said.

“We went out there on that date for a reason,” Webb said.

“There was some shock and surprise, as expected,” Webb said of Bentaas’ reaction to being arrested. “I know it sounds cliché, but we don’t quit on these. We never do.”

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