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Sheriff's department: Santee woman's murder solved through genetic genealogy testing

Investigative genetic genealogy has identified the killer of a Santee woman found dead in her apartment in 1988, the San Diego County Sheriff's Department announced Wednesday.

The stabbing death of 29-year-old Diane Lynn Dahn is the fifth local cold-case homicide solved through investigative genetic genealogy, sheriff's officials said. The process matches DNA collected at crimes scenes with samples submitted in public databases, often by people seeking to identify relatives.

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Advancements in DNA technology led to the eventual identification of a suspect, Warren Robertson, who lived in the same Graves Avenue apartment complex as the victim. Robertson died in an Indiana house fire in 1999, officials said.

Though a DNA profile of the suspect was compiled through fingernail scrapings and a hair found on the victim, no leads were generated as to the suspect's identity until recently. In 2020, a genetic genealogy investigation was undertaken, matching the suspect's profile against genetic profiles submitted on commercial databases, leading investigators to Robertson's direct descendants.

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San Diego Sheriff's Department
An undated photo of Diane Lynn Dahn released by the San Diego Sheriff's Department.

According to Sheriff's Homicide Crime Analyst Jeffrey Vandersip, the profile was matched against those of users who opted in and consented for law enforcement to conduct a genealogical analysis.

The technology gained large-scale notoriety through its use to identify the Golden State Killer, who was convicted and sentenced to life in prison for a series of murders and rapes in the 1970s and 80s. Most recently in San Diego County, the technology led to the identification of murder victim Laurie Diane Potter and the arrest last year of her then-husband, Jack Dennis Potter, who investigators believe killed her in 2003.

Sheriff's Homicide Detective Brian Patterson said he had "no doubt in my mind" that the Dahn case would have gone unsolved without genetic genealogy testing.

At a news conference announcing the case's resolution, Dahn's sister, Victoria Dahn-Minter, said she was "so grateful" to investigators for continuing to pursue the case after it went cold.

"I thought I myself was going to go to my grave not knowing (what happened)," she said.