How DNA and Genetic Genealogy Caught the Golden State Killer

DNA caught the Golden State Killer through a technique called investigative genetic genealogy: in 2018, investigators uploaded a DNA profile built from crime-scene evidence to the public genealogy database GEDmatch, found a distant cousin of the unknown suspect, traced family trees forward to Joseph James DeAngelo, and then confirmed the match by testing DNA he had discarded on his car door handle and in a tissue thrown in his trash. He was arrested on April 24, 2018, more than four decades after the crimes began.

First, DNA Proved the Crimes Were One Man’s Work

Before DNA could catch anyone, it had to show investigators who they were actually looking for. A serial burglar and rapist terrorized the Sacramento area from 1976 to 1979 under the name “East Area Rapist.” A killer operated in Southern California from late 1979 to 1986 under the name “Original Night Stalker.” Different jurisdictions, different task forces, different case files.

Biological evidence, mostly semen, had been collected from crime scenes over the years. Once forensic technology could develop DNA profiles from those older samples, analysts compared evidence across jurisdictions. Around 2001, DNA confirmed that the same man was responsible for both crime sprees.¹ The full scale of the case came into focus: at least 13 murders, more than 50 rapes, and scores of burglaries across multiple California counties.² Investigators now had one profile and one offender. They still had no name.

Why the National DNA Database Never Found Him

With a profile in hand, investigators ran it through CODIS, the FBI’s Combined DNA Index System. CODIS holds DNA profiles from convicted offenders, arrestees, and unsolved crime scenes, and it produces a name when a crime-scene profile matches someone already in the system.³

Nothing came back. DeAngelo had worked as a police officer in Exeter, California, starting in 1973, then at the Auburn Police Department near Sacramento until he was fired in 1979 for shoplifting. That misdemeanor never triggered DNA collection, and he had no qualifying conviction that would have placed his profile in the system.

CODIS also has a structural limit that mattered here. It uses Short Tandem Repeat analysis, which is designed to find exact matches or very close relatives. It cannot detect distant family connections like third or fourth cousins.³ So the evidence sat.

The Method That Finally Worked

The breakthrough came from a different kind of DNA profile and a very different database. Instead of the STR markers CODIS uses, investigators developed a Single Nucleotide Polymorphism profile from the crime-scene DNA. SNP profiles capture hundreds of thousands of data points across the genome. They are the same kind of profile a consumer ancestry service produces when a customer sends in a saliva sample.

By 2017, millions of people had uploaded SNP profiles to public genealogy databases such as GEDmatch to hunt for relatives and explore ancestry. If any of those users happened to be related to the unknown Golden State Killer, even distantly, a search would flag the connection. CODIS finds the suspect only when the suspect is already in it. Genetic genealogy finds the suspect through cousins the suspect has never met.

Building the Family Tree to Joseph DeAngelo

Investigators brought in Barbara Rae-Venter, a retired patent attorney who had become one of the country’s leading genetic genealogists. She worked alongside Paul Holes, a Contra Costa County cold-case investigator who had spent years on the case.

The team uploaded the perpetrator’s SNP profile to GEDmatch and pulled a list of genetic matches. The closest was a probable fourth cousin.¹ Fourth cousins share only a small fraction of DNA, but that sliver was enough to start the genealogical work. Rae-Venter and the investigators traced lineages backward through public records and historical documents to find common ancestors, then worked forward through descendants to identify living people who matched the killer’s likely age and geography.

The trail led to Joseph James DeAngelo, a 72-year-old former police officer living in Citrus Heights, a Sacramento suburb. He was the right age, had lived in the right places at the right times, and his law enforcement training was consistent with the offender’s evident familiarity with police procedure. That is a strong lead. It is not proof.

Confirming the Match With Discarded DNA

Asking DeAngelo for a sample would have warned him. Investigators used a settled rule instead: when someone discards an item in a public place, they abandon any privacy interest in it, and police can collect it without a warrant.⁴

On April 18, 2018, investigators swabbed the handle of DeAngelo’s car while it was parked at a Hobby Lobby in Roseville, California. Five days later, on April 23, they retrieved a tissue from the trash can outside his home. DNA from both items was compared to the original crime-scene profiles. The match was definitive. DeAngelo was arrested the next day, April 24, 2018.¹

Guilty Plea and Sentence

In June 2020, DeAngelo pleaded guilty to 13 counts of first-degree murder with special circumstances and 13 counts of kidnapping to commit robbery. He also admitted to 161 uncharged crimes involving 61 additional victims, including rape, attempted murder, burglary, and false imprisonment.²

He was sentenced to 11 consecutive life terms without the possibility of parole for the murders, plus an additional consecutive life term for the kidnappings and eight years for weapons enhancements.⁵

The Rules That Now Govern This Technique

The arrest was a forensic triumph and, almost immediately, a privacy controversy. People upload DNA to genealogy sites to find relatives, not to help police. And because relatives share DNA, one person’s upload effectively places their extended family in a searchable database without those relatives knowing.

In May 2019, GEDmatch changed its terms of service so that users must affirmatively opt in before their profiles can be searched by law enforcement. Before that, all profiles were searchable by default. Law enforcement users now work through a separate portal, GEDmatch PRO, which limits searches to profiles whose owners have consented.

That same year, the Department of Justice issued an interim policy on federal use of forensic genetic genealogy. It restricts the technique to unsolved violent crimes and unidentified human remains. Before investigators can upload a profile to a genealogy database, the DNA must first have been run through CODIS with no match, and the team must have pursued other reasonable leads. The policy also bars arresting anyone based solely on a genetic association from a genealogy service; investigators must obtain a direct sample from the suspect and confirm the match through traditional STR analysis before an arrest.⁶ Samples collected this way cannot be analyzed for disease risk or psychological traits.

Those guardrails, and the abandoned-DNA confirmation step that produced the arrest, are now the standard shape of the method that caught the Golden State Killer.

1
PubMed Central (PMC). Forensic Genealogy, Bioethics and the Golden State Killer Case
2
Contra Costa County, CA. News Release: Joseph DeAngelo Jr. Pleads Guilty to 13 Murders, 13 Kidnappings and Uncharged Crimes
3
Federal Bureau of Investigation. CODIS and NDIS Fact Sheet
4
National Institute of Justice. DNA – A Prosecutors Practice Notebook – Abandoned Sample
5
Tulare County District Attorney’s Office. Joseph James DeAngelo Jr. Sentenced to 11 Consecutive Life Terms Without the Possibility of Parole
6
United States Department of Justice. Interim Policy: Forensic Genetic Genealogical DNA Analysis and Searching