Growing up, Richard Hanchett heard stories about his biological mother — how beautiful she was, with red hair and blue eyes, and how much she loved singing.
“Just a really nice person,” Mr. Hanchett, 64, said.
But he never met Ruth Marie Terry. She chose to have him adopted right after he was born in 1958, entrusting him to a couple who worked with her at a plant that made door panels and seat covers for cars in Livonia, Mich. She was 21 at the time.
In 2018, hoping to find her, Mr. Hanchett, who lives in Waterford, Mich., took a DNA test through Ancestry.com and met her family in Tennessee. That’s when he learned that she had been missing since the early 1970s and that her relatives there had been searching for her for decades.
On Monday, the family finally learned what had happened to her when the F.B.I. announced that a badly mutilated body found nearly 50 years ago in the dunes of Provincetown, Mass., was that of Ms. Terry, who was 37 and originally from Tennessee.
On Wednesday, the authorities announced a new development in the investigation, saying that they were seeking information about a man, now deceased, named Guy Rockwell Muldavin, whom Ms. Terry was believed to have married shortly before she was murdered.
Mr. Muldavin, born in 1923, was a former antiques dealer who was arrested in 1960 in connection with the disappearance of his former wife and her daughter after mutilated remains, believed to be theirs, were found in their Seattle home, United Press International reported that year. Mr. Muldavin was given a suspended sentence in the case and was freed in 1962, The Associated Press reported.
Court records indicate that Mr. Muldavin married Ms. Terry in Reno, Nev., in February 1974, just months before she was killed.
Ms. Terry’s nephew Jim Terry said that the last time he had seen Ms. Terry was in July or August of 1973, in a motel room in Chattanooga, Tenn., with Mr. Muldavin. His mother thought she was going to California, and his father thought she was “headed up North,” Mr. Terry said.
“We never heard from her again,” said Mr. Terry, 60, adding: “I was a kid. I just remember a big smile and her auburn hair.”
Ms. Terry’s family later learned about Mr. Muldavin’s connection to the disappearance of his wife and her daughter in Seattle.
“It sure gave me the chills when I read that,” Mr. Hanchett said.
Last week, at the request of investigators, he submitted a DNA sample to confirm that the body found in Provincetown was that of his biological mother.
“I couldn’t believe when I found out who she was,” he said on Tuesday, one day after officials had briefed him on the breakthrough at an F.B.I. office in Troy, Mich. “And now I’m finding out where she was and what happened.”
Ms. Terry’s nude body was found on a beach blanket on Race Point Beach on July 26, 1974, by a girl who was hiking with her family. Ms. Terry’s hands were missing, presumably removed by her killer so she could not be identified with fingerprints, and her nearly severed head rested on folded jeans, the F.B.I. said.
Investigators said she had been killed by a blow to the head, probably several weeks earlier.
Detectives canvassed motels and rooming houses, reviewed thousands of reports of missing women, checked every vehicle licensed to drive on the dunes and used clay models to recreate what she might have looked like.
But they were unable to identify the woman they called the Lady of the Dunes, and her case haunted a generation of investigators and Cape Cod residents. She was said by the F.B.I. to have been the oldest unidentified homicide victim in Massachusetts.
As the trail went cold, some speculated that she had been killed by the notorious South Boston gangster James (Whitey) Bulger. The writer Joe Hill, a son of Stephen King, believed she might have been an extra from the movie “Jaws,” which was filmed on nearby Martha’s Vineyard that year.
In 2000, the authorities exhumed her remains from a cemetery in Provincetown to extract a DNA sample. But it wasn’t until recently that they were able to identify her through genetic genealogy, the same technique that was used to identify the Golden State Killer, among many others.
At a news conference on Monday, law enforcement officials said they were now turning their attention to finding Ms. Terry’s killer by tracing her history and asking the public for tips. They did not mention Mr. Muldavin. He died in 2002 at age 78 in Salinas, Calif., according to an obituary in The Monterey County Herald.
“It’s very likely that the person who did this is dead,” Michael D. O’Keefe, the district attorney for Cape Cod, Nantucket and Martha’s Vineyard, told reporters. “But they may not be, and so the message to them if they’re still out there is: ‘We’re coming.’”
Ms. Terry grew up in Whitwell, Tenn., about 24 miles northwest of Chattanooga, and left home when she was a teenager, Mr. Terry said. By the time she reached Livonia, Mich., she had been married once and separated, and was known as Ruth Smith, Mr. Hanchett said. She lived in California in the 1960s, Mr. Terry said, and then returned to Tennessee.
Mr. O’Keefe said there was no information to suggest that Ms. Terry had ever been reported to the authorities as a missing person. But Mr. Terry said that his sister, Marilyn Renee Hill, who died last year, had used genealogical websites and DNA tests to conduct her own investigation.
“My sister was kind of hellbent on trying to find her,” he said, “even in the later years.”
Mr. Hanchett, a retired software engineer for General Motors, said that he had helped Ms. Hill, searching online for names and addresses she would give him.
Mr. Hanchett said that Ms. Terry had tried to contact him once when he was about 13, but he rejected her overture, which he deeply regrets. He said he hoped to have her reburied next to her parents in Tennessee.
“Everybody that I talked to who knew her adored her,” he said. “I wish I could have just talked to her, touched her once.”
Alain Delaquérière and Susan C. Beachy contributed research.