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Son says he's "blown away" after DNA solves 1988 stabbing death of his mother

Tracing family trees to catch killers
Tracing family trees to catch killers 01:56

The San Diego Sheriff's Department said they have solved the 1988 killing of a woman, but the suspect died in an Indiana house fire more than two decades ago.   Genealogical DNA testing linked the suspect to Diane Dahn, 29, who was stabbed to death in her Santee apartment, county sheriff's investigators said at a news conference Wednesday .

When she failed to show up for work on May 2, 1988, a colleague from the San Diego Transit Corp. went to her home and found her body in her bedroom. Dahn's son, then 2 years old, was wandering in the apartment complex.

Investigators relied on testing of fingernail scrapings and a hair recovered from Dahn's hands, authorities said.

  Diane Dahn San Diego Sheriff's Department

Testing led investigators to Warren Robertson, a tow truck driver who lived in the same complex as Dahn. He died in an Indiana house fire in 1999 at age 39, authorities said.

"The investigation revealed substantial and convincing evidence that Robertson had murdered Diane," a sheriff's statement said.

It wasn't clear whether the two knew each other, but both were known to be racing enthusiasts and attended stock car races at the El Cajon Speedway, the statement said.

In a video statement, Dahn's now-grown son, Mark Beyer, said he was "blown away" by how the killing was solved.

Mark Beyer was only two years old when his mother was killed. San Diego Sheriff's Department

"Looking back some of the struggles you go through is you feel alone because of what you went through, you lost your mother," he said. "The answers that my family received is closure and closure is everything even after so much time had passed."

Dahn's younger sister, Victoria Dahn-Minter, said she was grateful that investigators had solved the case.

"I didn't think anything was ever going to come of this," she said at the news conference. "I thought I myself was going to go to my grave not knowing, as well as my mother and father."

It was the fifth cold-case killing solved through the use of genetic genealogy testing, sheriff's officials said.

The testing matches DNA from crime scenes to commercially available DNA databases in order to track down possible relatives of suspects. A cold case team formed family histories in the form of "trees," which led detectives to other potential relatives of the suspect.

"This process was so exhaustive, nine family trees were constructed with nearly 1,300 people connected to Robertson either through blood or marriage," the sheriff's office said. "This murder would likely have gone unsolved if not for the use of investigative genetic genealogy."

San Diego County Sheriff's Homicide investigators responded to the scene after the death of Diane Dahn. San Diego Sheriff's Department
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