For decades, the identity of the “Golden State Killer” remained a mystery. The individual was responsible for a crime spree across California from 1974 to 1986, including at least 13 murders and more than 50 rapes. Investigators had no viable leads to the perpetrator’s identity, and the case grew cold. A revolutionary investigative technique involving DNA finally broke the silence, leading to an arrest that brought the case to a close.
The Dead End in a Decades-Long Hunt
Investigators possessed the killer’s DNA, collected from multiple crime scenes. The standard procedure involves comparing the crime scene DNA profile to millions of others stored in the national DNA database, known as the Combined DNA Index System (CODIS). This database primarily contains DNA profiles from individuals convicted of felonies, as well as from arrestees in some jurisdictions.
The search for the Golden State Killer in CODIS, however, repeatedly came up empty. This lack of a match indicated the perpetrator likely had no prior felony convictions that would have required his DNA to be entered into the system. For investigators, this was a dead end. They had the killer’s genetic fingerprint but no one to match it to, and the case stalled for years, representing a failure of traditional forensic methods.
How Genetic Genealogy Identified the Suspect
The breakthrough came when investigators turned to a novel technique known as investigative genetic genealogy (IGG). Instead of relying on a criminal database, they uploaded the killer’s crime scene DNA profile to a public genealogy website called GEDmatch. This platform is designed for individuals seeking to build their family trees and find relatives by comparing their own DNA with others who have voluntarily submitted their genetic information. The goal was not to find the killer himself, but to find anyone who shared a significant amount of DNA with him.
The upload did not produce a direct match to the killer. Instead, it identified several of his distant relatives, including third and fourth cousins who had used the site for their own genealogical research. Working with genealogists, including Barbara Rae-Venter, they began building extensive family trees for these relatives. Their objective was to find a common ancestor shared by these individuals, and by extension, with the unknown killer.
By tracing these family lines forward through generations, they searched for a descendant who fit the known profile of the killer: a male of a certain age who had been in the specific geographic locations of the attacks. This genealogical work eventually led them to Joseph James DeAngelo, a former police officer. Investigators then covertly collected a DNA sample from DeAngelo, which matched the DNA from the crime scenes. This method, sometimes associated with the term “Howell,” demonstrated the power of combining public genetic data with genealogical research to resolve cases once considered unsolvable.
The Ethics of Forensic Genealogy
The capture of the Golden State Killer ignited a debate about the ethics of using public genealogy databases for law enforcement. The core issue revolves around genetic privacy and consent. Individuals who upload their DNA to sites like GEDmatch do so to explore their ancestry, not to become unwitting genetic informants against their relatives. By submitting their data, they inadvertently make their entire family tree searchable by police.
This raises questions about the balance between solving violent crimes and an individual’s right to genetic privacy. Critics argue that this method turns family members into “genetic witnesses” without their knowledge or permission. In response, many genealogy sites, including GEDmatch, updated their terms of service. Users are now required to explicitly “opt-in” if they are willing to allow their DNA profiles to be used in law enforcement searches, giving them direct control over how their information is utilized.