The turning point in the case, which highlights how DNA technology is increasingly being used to solve old homicides, came in 2009, Chief Burns said. That was when Michael Webb, a detective at the department, took the lead in pursuing the investigation using technology and databases that were not available to his predecessors.

[Why the arrest of a Golden State Killer suspect set off alarms among some scientists and ethicists.]

The case was “cold,” Detective Webb said at the news conference, but it was never “closed.”

“We don’t forget about these cases — we never do,” he said. “You work pretty hard when it is a child case.”

Ms. Bentaas is being held on murder and manslaughter charges, but the final charges will be determined by a grand jury or in a preliminary hearing on March 26, Crystal Johnson, a prosecutor working on the case, said in an interview on Tuesday. Ms. Bentaas is being held in Minnehaha County Jail with bail set at $250,000, according to records from the county sheriff’s office.

She had an initial appearance in front of a judge on Monday, Ms. Johnson said.

Raleigh Hansman, a lawyer for Ms. Bentaas, declined to comment on Tuesday, and calls to Ms. Bentaas’s family members were not answered.