Mad Over Stories Team For decades, some of the most disturbing murders in modern history sat in evidence lockers with a single frustrating problem: investigators had the killer’s DNA, but no name to match it to. Then, in 2018, a genealogy website cracked a case that had haunted California for over forty years — and quietly rewrote the rules of cold-case investigation.
The technique is called investigative genetic genealogy, and it has since closed dozens of cases once considered permanently unsolvable. Here’s how it works, and the real cases it has solved. If open cases are more your thing, see our roundup of the most baffling unsolved true crime cases.
How Genetic Genealogy Actually Works
Traditional DNA matching only works if the suspect’s profile is already in a law-enforcement database like CODIS. Genetic genealogy flips the approach: investigators upload crime-scene DNA to consumer ancestry databases (such as GEDmatch and FamilyTreeDNA, which permit law-enforcement use) and look not for the suspect, but for their relatives — cousins, second cousins, distant kin who voluntarily tested their own DNA. From those partial matches, genealogists build family trees backward and forward until the branches converge on one person who fits the timeline and geography. Police then confirm with a direct DNA sample. It’s detective work powered by the millions of people who’ve spat in a tube to learn their ancestry.
The Cases It Cracked
The Golden State Killer (2018) — the case that started it all
Between 1974 and 1986, a single offender committed at least 13 murders, more than 50 rapes, and 120 burglaries across California, evading capture for decades under names like the East Area Rapist and the Original Night Stalker. In April 2018, investigators used genetic genealogy on GEDmatch to trace crime-scene DNA to 72-year-old former police officer Joseph James DeAngelo. He pleaded guilty in 2020 and was sentenced to life without parole. The arrest proved the method worked — and triggered a wave of cold-case reopenings nationwide.
If that case pulls you in, the definitive account is journalist Michelle McNamara’s posthumously published bestseller — the book widely credited with helping reignite the investigation.
I'll Be Gone in the Dark
The obsessive, beautifully written hunt for the Golden State Killer that helped reignite the real case.
View on Amazon →The Bear Brook Murders — naming the unnamed
Genetic genealogy doesn’t only identify killers; it identifies victims. In New Hampshire’s decades-old Bear Brook case, bodies found in barrels went unidentified for years until genealogy helped put names to some of the victims and identify their killer, Terry Peder Rasmussen, a con man who had operated under multiple aliases.
The 1956 case of Patricia Kalitzke and Duane Bogle
In January 1956, a young Montana couple was found shot to death. The case went cold for 65 years — until, in 2021, investigators used a single preserved sperm cell and genetic genealogy to identify the late Kenneth Gould as the likely killer. At the time, it was reported as the oldest U.S. cold case ever solved with the technique.
Nancy Marie Bennallack (1970)
A 28-year-old court reporter was stabbed to death in her Sacramento apartment in 1970. For over 50 years the case sat unsolved, until genealogy identified Richard John Davis — who had, chillingly, died years earlier — as the man whose DNA matched the scene.
The Buckskin Girl and beyond
One of the earliest victim identifications came in 2018, when genealogy put a name — Marcia King — to a young woman found murdered in Ohio in 1981 and known for decades only as “the Buckskin Girl.” Her identification came just days before the DeAngelo arrest, and together the two cases announced the technique’s arrival.
The Ethical Questions It Raises
The method is powerful enough to make some people uneasy. When you upload your DNA to an ancestry site, you’re also exposing genetic information about relatives who never consented — including ones not yet born. That reality has fueled real debate about privacy, consent, and how far police should be allowed to reach into family trees built by ordinary people curious about their heritage. Most experts agree the technique has been a force for justice; the harder question is where the boundaries should sit.
Why This Matters for Every Cold Case
The lesson of the last few years is stark: a case being “unsolved” increasingly means “unsolved for now.” Evidence that sat useless for decades can suddenly speak, given a database large enough and a genealogist patient enough. For the families behind these cases, that’s changed everything. For a look at the mysteries still waiting for their breakthrough, read about the man who vanished in 1987 — and the kinds of clues that can resurface decades later.
Case details are drawn from public reporting and court records. Genetic genealogy identifications are investigative conclusions confirmed by direct DNA testing where noted.
Source: reference material.
