On a chilly February Sunday in 1980, a father and son panning for gold along Fly Creek in Clark County, Washington, kicked up the remains of a human skeleton that appeared to have been buried in a shallow grave. They called the authorities who came to collect the skull and what bones hadn’t been dragged away by animals, and were able to use the remains to construct a facial reconstruction that produced a picture of a teenage girl.

Detectives were able to deduce that she died from a cause that did not seem natural. Calls for information, searches through missing persons reports, and detective work turned up nothing. No one seemed to miss the teen, dubbed the ‘Fly Creek Jane Doe,’ and, for the last 40 years, that is as far as the case went–until now.

This summer Clark County detectives decided to post a DNA sample from the old remains to the Virginia-based Parabon NanoLabs, a public genealogy database that has had recent success closing old cold cases. The lab found a tie to a distant cousin of a teen named Sandra “Sandy” Renee Morden who said she was last seen in 1977–three years before her skeletal remains were found.

The Oregonian then dug up an old birthday announcement that was tied to the case. On April 29, 1977, in the classified section of the paper, a tiny ad appeared that said: “Sandra Renee Morden, Happy 15th Birthday. Love Always—Mom.” Such published greetings were a common way to mark a birthday or anniversary in the era before Facebook and other social media.

Morden’s parents were divorced, according to the DNA-linked cousin, who does not want to be named and who provided Clark County cold-case detective Lindsay Schultz with the only clues the teen’s life.

Schultz told the Oregonian that Morden was a “latchkey kid” who was mostly “unsupervised.” There is no indication that the parents filed a missing persons report, and, as Schultz says, “We didn’t have [the National Crime Information Center] at that time.”

The detective says Morden’s parents came from the San Francisco area and settled in Portland. They split up in the early 1970s, and did not communicate with each other. The girl’s mother, identified as Kathryn Irene Morden, apparently lost custody and the cousin said Sandy most often stayed with her father, identified as Andrew Bain Morden, a Marine Corps veteran who fought in the Korean War. Schultz says she likely fell through the cracks when one parent thought the other had her. She last attended Wilson High School in Portland.

Schultz told the Oregonian that the father likely thought she was with her mother. He had left her alone for an extended period of time and when he came back, she was gone, so he assumed she had gone to her mother’s home. “We don’t know for certain,” Schultz says. “We know that’s what family members believe.”

Both parents are dead, so there is no way to confirm what either of them knew. Schultz told the Oregonian that it is the birthday greeting that bothers him most. It was posted around the time the extended family says she disappeared.

“Was it just a mom who loved her daughter–or did her mom know something and put it out there for that reason?” Schultz said. “It’s one of those two, right? You ponder it. You look at it and you think, ‘What does it mean?’”

Now detectives are looking for the missing puzzle pieces. They are calling on anyone who might have any information about Morden, her parents, or how she might have died to contact the Clark County Medical Examiner's Office or Clark County Sheriff's Office Cold Case Tip Line.