Authorities said Wednesday that they had finally identified the body of a 16-year-old girl found strangled and sexually assaulted 45 years ago in the Woodlawn area of Baltimore County.

Known as the Woodlawn Jane Doe to cold case detectives for nearly five decades, Baltimore County police, using sophisticated DNA analysis that connected her body to relatives, identified the woman as Margaret Fetterolf of Alexandria, Va.

Fetterolf, described by a family member as a habitual runaway, went missing in the late summer of 1975. Her body, badly beaten with her hands bound, was found wrapped in a white sheet near a cemetery on Dogwood Road on Sept. 12, 1976.

Fetterolf’s identity and the circumstances of her murder had for decades confounded detectives, who even used pollen analysis for leads that took them as far away as Boston looking for clues.

Then they apparently turned to a new but controversial law enforcement technique — looking for potential relatives using DNA information uploaded to genealogy sites, including Ancestry.com. The technique went mainstream following its use in identifying the Golden State Killer in 2018.

Critics of the technique say it can turn family members into “genetic informants.”

Authorities would not disclose precisely how DNA was used in Fetterolf’s case, except to say that they received help from the National Center for Missing & Exploited Children and Bode Technology, a Lorton, Va., company that uses DNA to identify crime suspects and unidentified victims.

Edward Fetterolf, Margaret’s brother, said in an interview that police told him last month that they had identified his sister’s body with the help of DNA a relative uploaded to Ancestry.com. He was stunned.

“I asked the detective, ‘How did you get from an unsolved case to my phone number?’ ” Fetterolf said. “And he said it was all through genetics and Ancestry.com.”

Ancestry.com prohibits the use of their database by law enforcement for such purposes. It was not clear how police obtained the information, but a representative with Bode Technology said it is not unheard of for people to transfer their results to other databases that are accessible to police.

Fetterolf was 12 when his sister went missing for the final time.

“She was constantly running away,” Fetterolf said. “She was rebellious. She’d break the rules, get in trouble, run away.”

The family always held out hope that she would turn up — when she turned 18, when she turned 21, maybe on a holiday.

But she never did.

“After a while, you just assume the worst,” said Fetterolf, who is 57 and still lives in Alexandria.

Until police contacted him, Fetterolf had never heard of the Woodlawn Jane Doe. But now, he says he’ll do anything he can to help the police. He was able to recall some names of her old friends and boyfriends, which he gave to detectives.

“I hope somebody remembers something,” he said. “We want to know what happened to her.”

This story has been updated.