It was only three days into 1956 when three boys from Montana, out for a hike on a normal January day, made a gruesome discovery they were unlikely to ever forget.

During a walk near the Sun River, they found 18-year-old Lloyd Duane Bogle, dead from a gunshot wound to the head. They found him on the ground near his car, and someone had used his belt to tie his hands behind his back, according to a report from the Great Falls Tribune. The next day brought another disturbing discovery: A county road worker found 16-year-old Patricia Kalitzke's body in an area north of Great Falls, the paper reports. She had been shot in the head, just as Bogle had been, but she had also been sexually assaulted.

Their killings went unsolved until this week when investigators announced they had cracked what is believed to be the oldest case solved with DNA and forensic genealogy.

The victims were discovered in a lover's lane

Bogle, an airman hailing from Texas, and Kalitzke, a junior at Great Falls High School, had fallen for each other and were even considering marriage, the Tribune reports. The place where they were believed to have been killed was a known "lover's lane," according to a clipping from a local newspaper posted on a memorial page.

But their love story was brutally cut short by the actions of a killer whose identity would not be revealed for more than 60 years. And it was not for lack of trying: Early on in the case, investigators followed numerous leads, but none of them panned out. The case eventually went cold.

For decades, the Cascade County Sheriff's Office continued to work on it, with multiple detectives attempting to make progress over the years. One such investigator was Detective Sgt. Jon Kadner, who was assigned the case in 2012 — his first cold case, he said during an interview with NPR. He was immediately met with the daunting task of digitizing the expansive case file, an endeavor that took months.

He continued to work on the Kalitzke/Bogle case even while handling the newer cases that were landing on his desk all the time, but he had a feeling that more was needed to get to the bottom of what had happened to the couple all those decades ago.

"My first impression was that the only way we're gonna ever solve this is through the use of DNA," Kadner said.

Detectives turned to a new forensic investigation

Fortunately, Kadner had something to work with. During Kalitzke's autopsy in 1956, coroners had taken a vaginal swab, which had been preserved on a microscopic slide in the years since, according to the Great Falls Tribune report. Phil Matteson, a now-retired detective with the sheriff's office, sent that sample to a local lab for testing in 2001, and the team there identified sperm that did not belong to Bogle, her boyfriend, the paper reports.

Armed with this knowledge, Kadner in 2019 sought out the assistance of Bode Technology. After forensic genealogy was used to finally nab the Golden State Killer the year prior, law enforcement officials were becoming increasingly aware of the potential to use that technology to solve cold cases — even decades-old cases like Kalitzke and Bogle's.

With the help of partnering labs, forensic genealogists are able to use preserved samples to create a DNA profile of the culprit and then use that profile to search public databases for any potential matches. In most cases, those profiles can end up linking to distant relatives of the culprit — say, a second or third cousin. By searching public records (such as death certificates and newspaper clippings), forensic genealogists are then able to construct a family tree that can point them right to the suspect, even if that suspect has never provided their DNA to any public database.

In this case, "Our genealogists, what they're going to do is independently build a family tree from this cousin's profile," Andrew Singer, an executive with Bode Technology, told NPR. He called it "a reverse family tree. ... We're essentially going backwards. We're starting with a distant relative and trying to work back toward our unknown sample."

It worked: DNA testing led investigators to a man named Kenneth Gould. Before moving to Missouri in 1967, Gould had lived with his wife and children in the Great Falls area around the time of the murders, according to the Tribune.

"It felt great because for the first time in 65 years we finally had a direction and a place to take the investigation," Kadner told NPR. "Because it was all theories up to that point ... we finally had a match and we had a name. That changed the whole dynamic of the case."

Investigators' goal is a safer world

But there was one big problem: Gould had died in 2007 and his remains had been cremated, according to the Tribune. The only way to prove his guilt or his innocence was to test the DNA of his remaining relatives.

Detectives had an uncomfortable task ahead of them: letting a dead man's family know that, despite the fact that he'd never previously been identified as a person of interest, he was now the key suspect in a double homicide and rape.

Authorities traveled to Missouri, where they spoke with Gould's children and told them about the Kalitzke/Bogle case and eventually identified their father as a suspect, Kadner said. They asked for the family's help in either proving or disproving that Gould was the man responsible and the family complied.

The test results said Gould was the guy. With the killer finally identified, Kadner was able to reach out to the victims' surviving relatives and deliver the closure that had taken more than 60 years to procure. It was a bittersweet revelation: They were grateful for answers, but for many of the older people in the family, it was a struggle to have those wounds reopened.

"They're excited, but at the same time, it has brought up a lot of memories," Kadner said.

Now, the sheriff's office is considering forming a cold case task force, as other law enforcement agencies have done. The hope is that they'll be able to provide more families with the answers they deserve and, in many cases, have spent years waiting for.

"If there's new technology and we are able to potentially solve something, we want to keep working at it, because ultimately we're trying to do it for the family," he said. "Give them some closure."

The Kalitzke/Bogle case is one of the oldest criminal cases that has been solved using forensic genealogy, and authorities are hopeful that they'll be able to use this ever-advancing technology to solve cold cases dating back even further — although new state legislation restricting forensic genealogy could complicate matters.

Even without that complication, Singer explained to NPR, the success rate depends heavily on how well the evidence has been preserved over the years. Still, he hopes that it can be used to help law enforcement improve public safety and "[prevent] tomorrow's victim."

"It's really fantastic technology and it's going to solve a lot of cold cases," Singer said.