The year was 1974. A 26-year-old woman named Mary Schlais was found dead on a roadside in Dunn County, Wisconsin. She had been hitchhiking to an art show in Chicago, a common practice of the era, when her journey was violently cut short. For five decades, her file sat in a drawer, yellowing with time. Detectives followed hundreds of leads, but without a witness or a match in early fingerprint databases, the trail went cold.
Fast forward to March 2025, and a 84-year-old man named Jon K. Miller was sentenced to life in prison for that very crime. He wasn't caught because he slipped up in his old age; he was caught because the very definition of "forensic evidence" had evolved around him while he lived a quiet life in Minnesota.
To understand how a 50-year-old cold case finally saw justice, we must look at the radical evolution of forensic science—from the rudimentary blood typing of the 70s to the world-changing power of Investigative Genetic Genealogy (IGG).
Part I: The Stone Age of Forensics (1974–1985)
In 1974, when Mary Schlais was murdered, DNA was something scientists discussed in biology textbooks, not a tool for the courtroom. Investigators at the time relied on what is now considered "low-resolution" evidence.
Blood Typing and the ABO System
In the 1970s, the gold standard for biological evidence was ABO Blood Grouping. If a suspect left blood at a scene, police could only determine if they were Type A, B, AB, or O.
- The Limitation: Approximately 45% of the population is Type O. This meant that while blood typing could exclude a suspect (e.g., the killer is Type A, but the suspect is Type O), it could never identify one. It provided a "class" of people, not an individual.
Microscopy and "Junk" Science
Detectives also relied heavily on hair and fiber analysis. Analysts would look at hair found on a victim under a microscope to see if it "matched" a suspect’s hair. We now know, thanks to the
In the Schlais case, physical evidence was preserved, but the tools to read the "code" within that evidence simply didn't exist yet. The case was effectively frozen in time.
Part II: The Rise of the DNA Fingerprint (1986–2010)
The mid-80s brought a seismic shift. In 1984, Sir Alec Jeffreys at the University of Leicester discovered that certain areas of the human genome contain repeating sequences that are unique to every individual. He called this a "DNA Fingerprint."
The CODIS Era
By the 1990s, the FBI launched CODIS (Combined DNA Index System). This allowed law enforcement to upload DNA profiles from crime scenes and compare them against a database of known offenders.
- The Catch: CODIS only works if the killer is already "in the system." If a murderer like Jon K. Miller never committed another felony and never had his DNA taken, CODIS would return "No Match" forever.
For the Mary Schlais investigation, DNA was eventually extracted from her clothing and uploaded to CODIS. The result? Silence. The killer was a ghost.
Part III: The "Genetic Genealogy" Breakthrough (2018–Present)
The real revolution didn't happen in a police lab; it happened in the private sector. Companies like AncestryDNA and 23andMe created massive databases of people looking for their Irish roots or long-lost cousins.
How IGG Works: The Step-by-Step
In 2018, the arrest of the Golden State Killer proved that investigators didn't need the killer’s DNA in a police database—they only needed a third or fourth cousin to have taken a home DNA test.
- The SNP Profile: Standard forensic DNA (STR) looks at 20 locations on the genome. Investigative Genetic Genealogy looks at SNPs (Single Nucleotide Polymorphisms)—over 600,000 locations.
- The Upload: Police upload this "high-def" profile to public databases like GEDmatch or FamilyTreeDNA (where users can opt-in to help law enforcement).
- The Family Tree: Genealogists identify "matches"—people who share segments of DNA with the unknown killer. If two people share 3% of their DNA, they might be second cousins.
- Reverse Engineering: Experts like those at the Ramapo College IGG Center (who worked the Schlais case) build the family tree backward to find a common ancestor, then forward to find every living descendant who fits the suspect's profile.
Justice for Mary Schlais
In late 2024, the Dunn County Sheriff’s Department partnered with Ramapo College. By analyzing the DNA from 1974, they identified a cluster of relatives in Minnesota. The tree narrowed down to one man: Jon K. Miller. When confronted in November 2024, Miller—now an octogenarian—confessed. In March 2025, he was finally sentenced.
Part IV: The Ethical Frontier
As informational as this science is, it isn't without controversy. The transition from "private ancestry" to "police tool" has sparked a national debate on privacy.
- Privacy vs. Justice: Is it ethical to use a person’s DNA to arrest their cousin?
- The Abandonment Doctrine: Legally, courts have ruled that DNA left on a discarded coffee cup or napkin is "abandoned property," allowing police to test it without a warrant (see
Fourth Amendment Case Law
- Current Safeguards: Most platforms now require an explicit "Opt-In" for users who want their data to be searchable by police, ensuring that the "genetic dragnet" is a choice, not a requirement.
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