Jon Miller is charged with the murder of Mary Schlais in the 1974 cold case

The unsolved case of the murder of a Wisconsin hitchhiker was solved 50 years later thanks to a DNA breakthrough based on evidence collected from a hat left at the crime scene by the accused murderer.

Jon Keith Miller, 84, was arrested Thursday after “confirming his involvement” in the brutal stabbing of Mary Schlais, whose body was found at a Spring Brook intersection in February 1974.

Schlais, just 25 years old, had been hitchhiking to an art exhibition in Chicago when she was found dead that cold morning, and investigators were left with few clues other than one possible piece of evidence – a cap found near her body some hairs were pulled.

But for 50 years, police had little use for them until the Dunn County Sheriff's Office merged with the genetic genealogy department at Ramapo College in New Jersey, CBS News reported.

Using the hair, investigators were able to create a genetic profile and use it to identify potential relatives.

This process led to Miller's daughter, who then positively linked the hair's DNA to him.

When police interviewed Miller, who now lives in Minnesota, on Thursday, he initially denied knowing anything about the murder – but then presented them with the DNA evidence, which he admitted to.

The grizzled octogenarian said he saw Schlais hitchhiking on the side of the road that night and picked her up, according to the criminal complaint about his arrest cited by CBS News.

After he drove off, he began asking her for “sexual contact” — but when she refused, he pulled out a knife and began stabbing her in the back as she tried to defend herself, the lawsuit says Complaint.

He then stopped and began to hide her body in a snowbank, but when a car drove past, he panicked and ran – leaving behind the hat that would unsettle him five decades later.

“When he passed, the guy just stared at him. He said he would never forget the look on his face,” said Mary Dodge, whose neighbor Denny Anderson was the man who drove by and scared Miller off, CBS News reported.

Police said Miller was “fairly calm about the incident” when he confessed.

“I think it must even be a relief for him after living with it for 50 years. It must have been on his mind almost every day,” Dunn County Sheriff Kevin Bygd told reporters on Friday, according to CNN.

“You would think that would be the case for anyone with a conscience. So I think he personally had enough of fighting it.”

Bygd called the arrest “a huge victory for our department,” saying that for decades officers assigned to the cold case routinely came up empty-handed — and that without the help of Ramapo College, it might have remained that way.

“Agencies can spend thousands and thousands of dollars sending DNA samples to private labs across the country to try to get results, and we had a college that was very willing to get involved and help us in that process to help,” he said.

For years before Miller was implicated, Randall Woodfield was the prime suspect in the murder of Schlais – who was briefly a member of the Green Bay Packers but later went to prison for murder. He is suspected of being the “I-5 Killer,” who claimed numerous victims in the 1980s.