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She was found dead while hitchhiking in 1974. An arrest has finally been made.

An 84-year-old man confessed to his involvement in a 50-year-old cold case after authorities tracked him down using genetic genealogy.

Jon K. Miller, 84, was arrested last week in the homicide of 25-year-old Mary K. Schlais, Sheriff Kevin Bygd of the Dunn County Sheriff’s Office said during a press conference Friday afternoon.

He was arrested last week at his apartment in Owatonna, Minnesota, Bygd said.

“When confronted with the evidence, 84-year-old Jon K. Miller confirmed his involvement with Mary’s homicide in 1974,” Bygd said.

Miller is in custody at the Dunn County Jail, said Sheriff Bygd at a second press conference Monday afternoon. Authorities worked with the Investigative Genetic Genealogy Center, also known as IGG, at Ramapo College in New Jersey to reverse engineer the suspect's family tree and solve the case.

The victim, Schlais, was found dead on Feb. 15, 1974 in Spring Brook, a Wisconsin town about 260 miles northwest of Milwaukee.

While an eyewitness at the time reported seeing a suspect and suspect vehicle, authorities were unable to narrow down a suspect. Authorities followed up on tips and examined and reexamined evidence as DNA technology improved, but still, they had no suspect, Bygd said.

Victim was traveling to an art show when she was killed

Schlais was from Minneapolis, Minnesota. Back in February 1974, she was hitchhiking to an art show in Chicago, Illinois, Sheriff Bygd said at Friday's press conference.

Solving the Schlais case had been in the works for some time, said Sgt. Jason Stalker of the Dunn County Sheriff’s Office on Monday afternoon.

“If you've worked for this agency for any amount of time, you knew about Mary Schlais and her case,” Stalker said at Monday's press conference. “It is a very well known case within our agency, and was commonly a topic of discussion even after all of these years.”

Schlais was found with multiple stab wounds, and one piece of evidence found at the crime scene was a hat. Investigators had a feeling it would be vital in solving the case, so they collected the hat, he said.

Because DNA was fairly new in investigations such as these, investigators were only able to use the hat to gather hair samples, Stalker said. Investigators compared the hair samples to multiple others but no suspects were identified.

“As DNA technology advanced, there was eventually a partial male profile developed from the scrapings from the stocking cap,” Stalker said. “That profile was entered into CODIS, otherwise known as the Combined DNA Index System. There were no matches.”

With no matches, investigators learned their suspect had not been previously entered into the DNA database. Again, they were no closer to finding their alleged perpetrator.

Investigators worked with a college to solve decades-old case

Over the years, investigators tried multiple ways of narrowing down a suspect in the case. They even exhumed the victim’s remains to try and get new leads, said Sgt. Stalker of the Dunn County Sheriff's Office.

Dan Westlund, an investigator from the Dunn County Sheriff’s Office, spoke at both press conferences and, on Monday afternoon, said the team initially worked with Bode Technology to extract a DNA profile from hairs recovered from the crime scene.

The results were not enough to identify a suspect, so in fall 2022, investigators began working with Cairenn Binder and her team at Ramapo College in New Jersey, Westlund said.

Binder’s team identified an individual who could be related to the suspect, then investigators spent the next few months looking into this individual and others who could be related to the suspect. Each individual was ruled out, Westlund said.

“This exhausted any known male family members in this family lineage, which led to the hypothesis of an adoption in this known family line,” Westlund said.

On Oct. 19, Binder and her team gave investigators another name to look into and said the person may be able to help them identify their suspect, Westlund said. The individual agreed to use their genetic profile to help with the case, leading authorities to identify Miller as the DNA contributor and suspect.

Investigators identified Miller on Nov. 4, which would’ve been Schlais’ 76th birthday, Westlund said. He added that the suspect was not shocked to see authorities at his door.

“He did inform us that as soon as he had opened the door, he knew why we were there,” Westlund said about Miller.

When a local reporter asked authorities on Friday about a 2017 claim that there was a second DNA profile found during the investigation, the sheriff said that those contributors were eliminated as possibilities.

Nonprofit agency that helped solve case relies on DNA profile uploads, public records

Both Binder and David Gurney from Ramapo College's IGG Center spoke to the press Monday afternoon. Gurney said the team works with genetic profiles that have been uploaded to databases FamilyTreeDNA and GenBank.

Users take consumer DNA tests and upload them to find out more about their heritage or find new relatives, selecting an option to compare their DNA profiles to profiles law enforcement agencies upload, Gurney said.

IGG researchers also use public records such as census data to build family trees and identify common ancestors, then see where a DNA contributor may fit into a family tree, he said.

“It’s a lead that we turn over to law enforcement, like someone calling into a tip line,” he said, later adding that people who upload their DNA profiles help solve these cases.

The college’s IGG center is a nonprofit organization that opened its doors in 2022 and has trained over 150 individuals to do this type of research, Gurney said. Cases from law enforcement and medical examiner offices all over the country cross their desks, he said.

Since 2022, the group has provided leads in 17 cases, he said.

Mary Schlais, whose body was found in Dunn County, Wisconsin on Feb. 15, 1974.
Mary Schlais, whose body was found in Dunn County, Wisconsin on Feb. 15, 1974.

It wasn’t unusual to hitchhike back in 1974, sheriff says

Bygd said that in 1974, hitchhiking wasn’t unusual, but stories like this are the reason it’s no longer a common practice.

“(Schlais) was a very bright young lady who had a very bright future ahead of her and her life was taken away from her way too young,” Sheriff Bygd said.

He added that he believes the suspect, who is 84, will spend the rest of his life in prison.

According to Westlund, the investigator who worked on the case, the victim's family is relieved that an arrest has been made.

“We don't want to forget that this is about justice for Mary and bringing her family closure,” he said. “Mary can be remembered as an accomplished artist, equestrian, sister and daughter.”

This story has been updated to add new information.

Saleen Martin is a reporter on USA TODAY's NOW team. She is from Norfolk, Virginia the 757. Follow her on Twitter at @SaleenMartin or email her at sdmartin@usatoday.com.

This article originally appeared on USA TODAY: Authorities arrest man, 84, in cold case murder of Mary K. Schlais