The following day, three boys hiking along the Sun River in Great Falls found Mr. Bogle’s body in an area that was known as a rendezvous spot for teenagers.
He was face down, and had been shot in the back of the head. His hands had been 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 Ms. Kalitzke had been kidnapped.
But the next day, Jan. 4, 1956, a county road worker found her body off a gravel road about five 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, Sergeant 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. Mr. Bulger, who died in 2018, had lived in Great Falls in the 1950s and had been arrested in a rape there in 1951, Sergeant 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,” Sergeant Kadner said.