On a Tuesday evening in April 2018, seventy-two-year-old Joseph James DeAngelo was arrested outside his Citrus Heights home. Formerly a police officer, DeAngelo stood accused of thirteen murders, fifty-one rapes, and over one hundred burglaries committed across California between 1974 and 1986 [2]. What made this case remarkable was not the arrest itself but how it happened: investigators had used a publicly accessible genealogy database to identify DeAngelo as a suspect, a technique that would reshape criminal investigations and trigger fierce debates about privacy in the genomic age.

Investigative genetic genealogy, the method behind DeAngelo's capture, combines traditional genealogical research with DNA analysis to identify suspects through their family relationships [1]. The process begins when law enforcement uploads crime scene DNA to public genealogy databases like GEDmatch or FamilyTreeDNA. These platforms allow users to compare genetic material and identify relatives through shared DNA segments known as identity-by-descent (IBD) fragments [6]. From there, genealogists construct family trees using public records and historical documents, gradually narrowing the pool of potential suspects until they reach an individual whose profile matches the crime scene DNA.

How Investigative Genetic Genealogy Works

As of December 2023, this technique has solved 651 criminal cases and identified 318 individual perpetrators [1]. An additional 464 decedents have been identified through the method, along with four living individuals previously unknown to authorities [1]. These numbers represent a remarkable expansion of investigative capacity for cases that might otherwise remain forever unsolved.

The Scale of Cases Solved

Parabon NanoLabs, a biotechnology company, has emerged as the leading practitioner of investigative genetic genealogy. By May 2020, the company had participated in nearly 500 cases and achieved 109 confirmed suspect identifications [4].

The Leading Practitioner: Parabon NanoLabs

The first conviction secured through genetic genealogy occurred in June 2019, when William Earl Talbott II was found guilty of two counts of first-degree murder in Washington state [4]. These cases demonstrated that genetic genealogy could produce legally admissible evidence capable of securing convictions.

From Identification to Conviction

The Golden State Killer investigation relied on GEDmatch, a public genealogy platform founded in 2010 that had accumulated approximately 1.45 million DNA profiles by Fall 2020 [3]. The dataset's power lies in its coverage: data from roughly 1.2 million individuals can identify a third cousin or closer in over 90 percent of the population [1]. By October 2020, GEDmatch had contributed to approximately 150 arrests in cold cases [3]. The platform's role in identifying DeAngelo brought the technique into mainstream awareness and prompted questions about the governance of genetic data.

GEDmatch and the Golden State Killer

Privacy concerns have shadowed investigative genetic genealogy since its emergence. More recent controversies have centered on the permissions granted to law enforcement when accessing genealogy platforms.

FamilyTreeDNA faced significant backlash after admitting in 2019 that the company had been working secretly with the FBI since 2018, providing investigators with access to user profiles without requiring warrants [1]. This disclosure revealed a fundamental tension: users who uploaded their DNA seeking to connect with distant relatives might not have anticipated that their genetic information could become a targeting mechanism for criminal investigations.

GEDmatch responded to the Golden State Killer case by requiring users to opt-in explicitly before allowing law enforcement access to their profiles [3]. However, a November 2019 Florida judge approved a warrant that required GEDmatch to reveal users who had not opted in, effectively negating the consent mechanism for those individuals [3]. Practitioners at GEDmatch had also previously helped law enforcement access data from users who had explicitly opted out, violating the platform's stated policies [1].

Privacy and Consent Concerns

The United States Department of Justice released interim guidelines in September 2019 limiting investigative genetic genealogy to violent crimes such as murder and rape, reflecting concerns about the scope of the technique's application [3]. Yet the guidelines are administrative in nature rather than legally binding, leaving significant ambiguity about future regulation.

A structural bias complicates the equity of investigative genetic genealogy. The CODIS database maintained by the FBI contains genetic profiles from approximately 18 million convicted felons and arrestees, but representation is uneven across populations [1]. Direct-to-consumer genealogy databases show a different pattern in demographic coverage [1]. This asymmetry means that investigative genetic genealogy proves most effective in some contexts more than others, raising questions about whether the technology widens or narrows existing disparities in criminal justice outcomes.

Equity and Regulatory Questions

Researchers have noted that the technique should theoretically help reduce racial disparities in unsolved cases by expanding the pool of potential matches beyond convicted populations [1]. Yet most victims identified through investigative genetic genealogy have been white, suggesting that implementation has not fully realized this potential [1].

The scientific foundation for investigative genetic genealogy rests on peer-reviewed research demonstrating that genomic data can identify individuals through long-range familial searches and that identity-by-descent segments reveal shared ancestors [6]. This methodology has been validated through hundreds of successful identifications, though the probabilistic nature of genetic relationships means that interpretation requires careful genealogical work rather than simple database matching.

The Scientific Foundation

Investigative genetic genealogy represents a genuine transformation in the capacity to solve violent crimes where traditional methods have failed. Cold cases spanning decades have been resolved, perpetrators have faced accountability, and families have received answers that seemed permanently out of reach. Yet the technique operates in a legal and ethical environment still catching up to its implications. Questions about consent, data governance, and equity remain unresolved, and the framework governing this investigative power continues to evolve as courts, legislatures, and technology companies navigate competing interests. The capture of the Golden State Killer demonstrated what is possible; the harder question of what should be permitted remains answered only in part.