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A statutory rape case — that included a placenta sample seized from an abortion clinic as evidence — was dropped against a 27-year-old man in South Dakota.

But the man still faces another, similar charge involving a girl under 13 in a different county.

Nathan Hankins had been charged with rape in the fourth degree after a 16-year-old girl told an abortion clinic in December 2018 that she had become pregnant by him when she was 15. The age of consent in South Dakota is 16.

Pennington County prosecutors dropped the charge just before jury selection was supposed to begin this week, lawyers on both sides said.

Hankins remains in jail in Lawrence County on a more serious rape charge, involving a "child under the age of thirteen," according to a grand jury indictment. Conviction on all charges could land him in prison for life, authorities said.

Nathan Hankins. Lawrence County Sheriff's Office

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Hankins' case in Pennington County drew attention because of biological material that prosecutors intended to use against him.

When the alleged victim had an abortion in Colorado, she told medical professionals she was 15 when she became pregnant by her then 25-year-old boyfriend, Hankins. The clinic notified police and South Dakota investigators were given a sample of the placenta.

Hankins' defense lawyer, who told NBC News that the placenta allegedly proved his client's paternity, challenged the evidence in court on the basis that it was obtained without a warrant.

A trial judge denied this challenge, ruling the evidence was admissible.

Then this week, Pennington County prosecutors dropped the rape charge over concerns that they could not absolutely prove that Hankins and the then-underage girl had sex in that county, according to the county's chief deputy state's attorney, Lara Roetzel. The victim has not been cooperative with authorities, she said.

And with Hankins facing another charge of statutory rape in a different county, there was no immediate concern of him walking away free, authorities said.

Defense lawyer Paul Pietz said he was happy for Hankins that the one case was dropped, but disappointed he did not have an opportunity to appeal the ruling that allowed the seized placenta as evidence.

“From the point of view of my client, this is a good thing," Pietz told NBC News. “But for the bigger picture, it could have been good to have this appealed."

Arthur Caplan, founder of the Division of Medical Ethics at the New York University School of Medicine, said he believes the clinic erred on ethical grounds in surrendering the biological material without a warrant.

"The woman said she was raped," by admitting to underage sex with the defendant, Caplan said. "But she didn’t ask them to do anything about it. So they don't have her permission or consent" to use her biological material.

Caplan said the patient, having reached the age of consent by the time of the abortion, should have been allowed to tell doctors not to give away the placenta.

“She controls where or if that information gets on to the police," he said.