She vanished decades ago. Her children just learned she had been killed.

One day, about a half-century ago, William Heiser Jr. came home from boarding school to find that his mother was gone. His father, William Sr., a former police officer, told him and his sister that their mother had walked out.

“He just said she just packed up her stuff and left,” Heiser said, even though some of her clothes and belongings were still in their house in Philadelphia.

Heiser, 68, said he figured that his parents had grown apart or divorced. Sometimes, he wondered if his mother had been upset at him and his sister. As the years went on, the disappearance of his mother, Marie Petry Heiser, became more painful, as Heiser and his sister questioned why she never called or wrote. When they asked their father where she was, he would tell them he didn’t know.

“‘I haven’t heard; I don’t know where she’s at,’” the elder Heiser would tell them, the son recalled. “We had no reason to question him because we hadn’t heard neither.”

Now, the long mystery of Marie Heiser’s disappearance has been solved — at least in part.

This past week, police announced that Marie Heiser was the victim of a homicide and that her remains had been discovered more than 40 years ago, in June 1977, by a teenager who was biking home in a wooded area of Townsend, Delaware, about 65 miles south of the Heisers’ home in Philadelphia.

Those remains had never been identified, but they were recently connected to Heiser through DNA technology that traced her family tree back to her children. The police said they were continuing to investigate how she had been killed and had not identified a suspect.

Heiser, who was 50 when she died, was never reported missing, and the elder William Heiser died in 2006. The police said his explanation that Marie Heiser had left the family was one of many questions they were investigating.

“We’re looking into every aspect of the case and, trust me, that has not passed us,” said Master Cpl. Michel Eckerd of the New Castle County Police Department in Delaware.

The younger William Heiser said he was certain that his father had nothing to do with his mother’s disappearance.

“He would be the last person that would ever hurt anybody,” said Heiser, who followed his father into law enforcement and is retired from the Volusia County Sheriff’s Department in Florida. “He was a saint — took care of his family, never raised his voice or hands or argued or anything.”

Marie Heiser was a homemaker and a part-time employee at the former Ashbourne Country Club in Cheltenham, Pennsylvania, in the 1970s, the police said. Eckerd said he hoped someone in the public who knew her or the family would come forward with information.

“She was very involved in the community in Philadelphia,” he said.

Heiser said he remembered going to the Jersey Shore and strolling along the boardwalk with his mother.

“She took care of us, and we had good times when I was smaller,” he said. “She was just a good person.”

William Heiser Sr. was a member of the Philadelphia Police Department’s Highway Patrol from the 1950s until the early 1960s, the police said. The patrol was known for performing thrill shows in stadiums and arenas, and Heiser had to leave the force after being seriously injured while rehearsing for a show, police said.

He went on to work as a truck driver and moved to South Daytona Beach, Florida, in the late 1970s, police said.

In June 1977, the New Castle County Police responded to the discovery of a woman’s remains in the Townsend area. The Delaware medical examiner determined at the time that the woman was the victim of a homicide, and police conducted an extensive investigation.

But authorities could not identify her or obtain any leads, police said. The case went cold, as fingerprints and dental records failed to turn up any matches.

Then, in 2008, investigators extracted a DNA profile from the remains. But, police said, the DNA failed to lead to a match after it was entered it into a national database.

In February 2017, police sent the sample to a Virginia company, Parabon NanoLabs, where a forensic artist, Thom Shaw, used the sample to create a sketch of the victim. The lab also mapped her potential family tree.

In 2019, a police officer in Montgomery County, Maryland, Steven Smugeresky, took over the ancestry research and worked tirelessly to develop leads on the identity of the remains, police said. The New Castle County Police followed up on those leads and obtained DNA samples from possible relatives.

Heiser said he got a call about two months ago from an investigator who asked him for a DNA sample and explained, “We think we might have found your mother’s remains.”

“It was a shock to us,” he said. “You’re never expecting a phone call like that, ever.”

A few weeks later, he said, police called him again to say the remains had been conclusively identified.

“You’re thinking, ‘Well, as horrible as this story is, there’s some closure,’” he said.

But the discovery has also raised more questions, he said, about who might have killed his mother.

“Before, we wondered where our mother was,” he said. “Now, we’re wondering what happened to our mother. So one door closes, another opens.”