For 43 years, she was known only as Jane Doe No. 40, a strangulation victim whose body was discovered in a shallow grave near Lake Merced by a boy who was digging around for turtle eggs.

But DNA tests — and a missing person report filed in 2017 — gave authorities what they needed to finally learn who the victim was: a 14-year-old girl named Judy Gifford.

Now, San Francisco police are trying to find out who killed her.

The identification provided some answers to the girl’s half brother, William Shin, a Maryland man who filed the missing person’s report on Judy in 2017, telling San Francisco police that he “remembered having a sister when he was a child,” according to New Jersey State Police, who assisted San Francisco police in the investigation.

“He told investigators that his sister went missing when she was 14 years old, and his family had not seen or heard from her since 1976,” the New Jersey agency said.

On the Websleuths site in which his sister’s case was discussed by various registered users, a commenter who identified himself as Shin laid out a detailed story, along with photos, behind the mystery of Judy’s disappearance. The Chronicle is trying to reach him for comment.

Judy had moved to San Francisco in the summer of 1976 to live with her father, his wife and her two half siblings: Shin, who was 6, and his sister, who was much younger, according to the post.

The family lived in Park Merced. Soon, Judy was gone — and Shin was told that she had returned to New Jersey to her aunt, Ogee Gifford, who had previously been caring for her.

It was only years later, according to the post, that Shin, then 18 years old, visited his aunt in New Jersey and learned that Judy had never returned to live with her.

The body that 43 years later would be identified as Judy’s was discovered near Lake Merced on Oct. 1, 1976, by a 17-year-old boy.

According to a Chronicle story published on Oct. 2, 1976, the boy, Donald McIsaac, noticed a human hand protruding from the sand behind a pumping station. He told police he had captured a turtle and was digging for eggs when he found the girl’s body “six inches below the surface of sandy soil about 20 feet from the lake shore.”

The body was “badly decomposed,” police told The Chronicle at the time.

It had been buried in the shallow grave for two to four weeks, possibly up to six weeks, police said. San Francisco investigators called the unidentified victim Jane Doe No. 40 and determined that she had been strangled.

Police described the victim as a petite, brown-haired girl, between 14 and 20 years old.

She was fully dressed and wearing gold earrings and a Timex watch. Police released a photo of an owl necklace found in her pocket, hoping someone could help identify her.

No one did.

An investigation began earlier this year after police combed through unsolved missing persons cases and found the report filed in 2017 — seeing that Judy had disappeared in San Francisco around the same time Jane Doe No. 40 was killed.

In June, a San Francisco investigator contacted New Jersey State Police and the Anne Arundel County Police Department in Maryland and requested their help in getting DNA samples from Gifford’s aunt and half brother for comparison with the DNA collected from Jane Doe No. 40.

Detectives also collected photographs and dental records. In some of the photographs of Gifford, detectives noticed she was wearing a gold chain with an owl pendant that matched the jewelry found on Jane Doe No. 40 in San Francisco, officials said.

The California Department of Justice Missing Persons Laboratory determined that the unidentified victim’s familial DNA matched that of her aunt.

On Nov. 22, New Jersey State Police detectives Erin Micciulla and Jeff Greco visited Ogee Gifford’s home to deliver the news that her niece was the cold case homicide victim.

“Ms. Gifford, who has never changed her phone number in case her niece ever called, was brought some closure as a result of the joint effort,” New Jersey State Police said.

Reached by phone on Friday, Gifford, 87, said a detective had recently visited her home and she was glad police identified Judy. She declined to comment further.

The investigation into Judy’s death remains open.

Anyone with information about Judy’s disappearance or death can call the San Francisco Police Department’s tip line at 415-575-4444, or text a tip to TIP411 by beginning the message with “SFPD.” Callers can remain anonymous.

Chronicle staff writer Evan Sernoffsky contributed to this report.

Lauren Hernández is a San Francisco Chronicle staff writer. Email: lauren.hernandez@sfchronicle.com Twitter: @LaurenPorFavor