When Detective Sgt. Jon Kadner of the Cascade County Sheriff’s Office in Montana was told in 2012 that he was being put in charge of the investigation into a long-unsolved double homicide, the case was already more than 50 years old.

It was the first time that Kadner, who is 40 and grew up in small-town Iowa, had heard of Duane Bogle and Patricia Kalitzke, teenage sweethearts who had been fatally shot in January 1956, more than two decades before he was born, presumably after they drove to an area known as lovers’ lane in Great Falls.

“There was just years and years of documentation and numerous suspects that had been looked into,” Kadner said. “But I knew the key was going to be DNA.”

On Tuesday, the Cascade County Sheriff’s Office announced that it had cracked the case. The office identified Kenneth Gould, a horse trainer who died in 2007 at age 79, as the “likely suspect” who had shot and killed Bogle, 18, and Kalitzke, 16, more than 65 years ago.

Kadner said he believed it was the oldest homicide case in the United States to be solved with genetic genealogy, which uses DNA from crime scenes to identify the relatives of potential suspects and eventually the suspects themselves.

John Butler, an expert on forensic genetics at the National Institute of Standards and Technology, said while he was not aware of any group that officially tracks cold cases, “Certainly, 1956 is the oldest that I have heard about up to this point.”

The investigation involved painstaking research into a long-ago crime that had once generated national media attention.

Kalitzke was a junior at Great Falls High School. Bogle, an airman from Waco, Texas, was stationed at nearby Malmstrom Air Force Base. They both loved dancing and music, and he was “instantly smitten with Patty,” when they met in December 1955, Kadner said.

The teenagers were last seen at Pete’s Drive-In restaurant in Great Falls, just after 9 p.m. on Jan. 2, 1956. When they didn’t come home that night, their families assumed they had eloped, Kadner said.

The next day, three boys hiking along the Sun River in Great Falls found Bogle’s body in an area that was known as a rendezvous spot for teenagers.

He was facedown and had been shot in the back of the head. His hands were tied behind his back with his own belt. The ignition switch, radio and headlights on his car were on, and the car was in gear. His expensive camera had not been taken.

Investigators initially feared that Kalitzke had been kidnapped.

But the next day, Jan. 4, a county road worker found her body off a gravel road about 5 miles north of Great Falls. She had been shot in the head and had injuries that were consistent with a struggle or a sexual assault, Kadner said.

Newspaper headlines described the teenagers as “lovers’ lane slaying victims” and recalled a “wide search” for a “brutal killer.”

Over the next half-century, detectives investigated about 35 potential suspects, including James (Whitey) Bulger, the notorious South Boston mobster who was convicted in 2013 of participating in 11 murders. Bulger, who died in 2018, had lived in Great Falls in the 1950s and had been arrested in a rape there in 1951, Kadner said.

But no one was ever charged, and the case went cold.

Investigators turned to genetic genealogy in 2018, after the authorities arrested Joseph James DeAngelo, known as the Golden State Killer and accused him of committing 13 murders and nearly 50 rapes that terrorized California in the 1970s and ’80s. It was the first high-profile case to be cracked with genetic genealogy.

“That’s when we really started looking at what evidence we had and if we could potentially do the same thing,” Kadner said.

Kadner said the crucial piece of evidence was a DNA sample from a sperm cell that had been collected from Kalitzke’s body during her autopsy. That sample had been preserved in an evidence vault for six decades.

In 2001, it had been sent to the state crime lab for analysis, but it did not lead to any matches in a national criminal database.

In 2019, with the help of Bode Technology, a Virginia company that specializes in DNA analysis, another DNA profile was extracted from the sample, which enabled investigators to build a family tree that led them to Gould, Kadner said.

Because Gould had been cremated, investigators collected DNA from his children, which linked Gould to the sperm cell that had been found on Kalitzke’s body, Kadner said.

Gould, who was 29 in 1956, lived just over a mile from Kalitzke’s house and kept horses about 600 yards from the house where she had grown up, Kadner said. He had married another 16-year-old girl in 1952 and eventually had five children.

After the killings, he left the area and was seen living in two other Montana towns before moving to Alton, Missouri, in 1967.

Kalitzke’s sister has advanced dementia, Kadner said.

Bogle’s family contended for years with “crazy stories” about what might have happened, including rumors that he might have been mixed up with the mob, said Caryn Bogle McCarthy, 54, whose father, James Bogle, was Duane Bogle’s younger brother.

Now that authorities have a suspect, “it conclusively allows to us to stop wondering,” she said.

But the resolution, she said, had also reopened pain from that era, particularly for an older generation that knew Bogle as funny and charming — “the one that everybody in my family loved.” She said her aunt had been in tears all week. Her father, who died in 2013, had “idolized Duane,” as a boy, she said.

“It’s like it just happened yesterday,” McCarthy said. “So if I was asked is this great modern technology a great thing, I would say, on balance, yes, for my generation, a generation once removed. But it definitely reopens old wounds that have had a chance to crust over.”

This article originally appeared in The New York Times.

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