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Police Say DNA Tracing Has Identified Killer in 1988 Cold Case Murder of San Diego Woman, 29

Warren Robertson, Diane Dahn

Warren Robertson (L), Diane Dahn (R) appear in images released by the San Diego County Sheriff’s Department.

Investigators in San Diego say they’ve identified the man who stabbed a woman to death in 1988 in her own home.  The woman left behind a two-year-old son who was later found wandering around the apartment complex where the victim, her son, and the alleged murderer all lived.

The body of Diane Lynn Dahn, 29, was discovered in her Santee apartment on May 2, 1988, by a coworker who had stopped by after Dahn didn’t show up for her shift at the San Diego Transit Corporation.

Dahn was found bludgeoned and stabbed in her bedroom. Her two-year-old son, Mark Beyer, was found wandering in the apartment complex.

An autopsy determined that Dahn died from stab wounds to the chest, and her death was determined to be a homicide.

The case remained unsolved until a genetic genealogy investigation in 2020, which led authorities to identify the suspect as Warren Robertson.

Although cold case detectives couldn’t determine whether Robertson and Dahn knew each other, Robertson, originally from Arkansas, was living in the same apartment complex as Dahn at the time of her murder.

Authorities say that Robertson and Dahn were both racing enthusiasts who attended stock car races at the same area racetrack.

Robertson was a local tow truck driver, authorities say. He left his family in San Diego after Dahn’s death and eventually moved to Indiana in 1989.

At age 39, Robertson died in a house fire in November 1999.

Beyer, Dahn’s son, said in a press release that the identification of Robertson has brought him a degree of closure.

“Looking back some of the struggles you go through is you feel alone because of what you went through, you lost your mother,” Beyer said. “You know you have family, you know you have family who loves you, but sometimes you do feel alone all the time. Just good work for the Homicide Unit that I was so blown away when I heard the story of how it actually transpired. Like how you go from what little information you have to building a case like that was truly impressive. The answers that my family received is closure and closure is everything even after so much time had passed.”

The identification of Robertson as Dahn’s likely killer comes just weeks after what would have been Dahn’s 63rd birthday.

According to a statement from the San Diego County Sheriff’s Office, an “extensive investigation” was conducted after Dahn’s death, but no suspect was identified.

Investigators revisited the case in 2000 and 2001 with DNA samples taken from Diane’s fingernails, but the sample was insufficient and couldn’t be added to a federal database of DNA from unsolved crimes.

In 2010, a cold case team from the sheriff’s department reviewed the case for additional leads and processed a hair that had been found in Dahn’s hand. The DNA from that hair was consistent with the sample found under her fingernails, the sheriff’s department said, but there were no matches found in the federal database.

A break came in May 2020, after the sheriff’s department turned to investigative genetic genealogy, which found relatives whose DNA profile matched the DNA of the as-yet-unidentified suspect in Dahn’s murder.

“The San Diego County Sheriff’s Department is committed to bringing answers to families no matter how long ago the crime occurred,” Acting Sheriff Kelly Martinez said in the Sheriff Department’s press release. “I commend the Sheriff’s Homicide Unit and Crime Lab for doing an amazing job of collecting and preserving evidence nearly 34 years ago that was able to be used today. I also want to thank our Cold Case Detectives and Analysts in the Sheriff’s Homicide Unit for relentlessly pursuing justice. They kept reviewing Dahn’s case using modern DNA technology. I hope this brings some sense of peace and healing to the victim and her family.”

Dahn’s sister, Victoria Dahn-Minter, said that she was relieved to have answers, even though knowing who likely killed Diane doesn’t alleviate the pain of losing her.

“Thirty-four years is a long time to be in a state of grief and immense sorrow,” Dahn-Minter said. “Not knowing almost consumed me. My sister was an amazing person, she loved life and always played the violin and guitar. It’s unfortunate my nephew never had the chance to know his mom. She was a great mother. The detectives did such a wonderful job. They were persistent. Whenever I would call to follow up, they knew Diane’s name and her case right away. I didn’t think anything was ever going to happen. It doesn’t make the pain go away, but at least there’s an answer.”

[Images courtesy San Diego Sheriff’s Department.]

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