SAN DIEGO — A nearly 34-year-old cold case has finally been cracked by the San Diego County Sheriff’s Department. 

The department used investigative genetic genealogy to help identify a suspect in the East County murder of Diane Dahn in 1988.

“It’s been a long process,” Diane’s sister Victoria Dahn-Minter said Wednesday as she broke down in tears. “I didn’t think I was going to do this. I didn’t think anything was ever going to come of this. I thought I myself was going to go to my grave not knowing.”

On May 2, 1988, Dahn never arrived for work at the San Diego Transit Corporation, the department said. A coworker went to her apartment in the 8700 block of Graves Avenue in Santee around 1:30 p.m. and found Dahn stabbed to death inside her bedroom. Dahn’s 2-year-old son was found wandering the complex. 

“Some of the struggles that you go through, you kind of feel alone because of the struggles you went through,” Dahn’s son Mark Beyer said. “You know you lost your mother. You know you have family. You know you have people who love you but sometimes you do feel alone all the time.”

But time wouldn’t stop homicide detectives who kept his mother’s case by matching her murderer’s DNA samples with samples from commercial genealogy databases, which led them to suspect Warren Robertson.

“This assistance proved to be the break we needed to identify the suspect in Diane Dahn’s murder,” said San Diego County Sheriff’s Homicide Crime Analyst Jeffrey Vandersip.

Detectives say Robertson died in 1999. According to the sheriff’s department, he was an Arkansas native who spent his younger years in the San Diego area. In 1988, he was living in the same apartment complex as Dahn and working as a tow truck driver.

Investigators say he left his family and moved to Lakeside after Dahn’s murder and later relocated to Indiana in 1989, where he remained until he died in a house fire at age 39.

DNA testing determined that he was the donor of previously unknown DNA found from samples taken from Dahn’s fingernails and a hair that was found in her hand.

It’s not clear if Dahn and Robertson knew each other. The sheriff’s department noted both were “race enthusiasts” and attended races at the El Cajon Speedway around the time when Dahn was killed.

But after nearly 34 years, Dahn’s family has some answers.

“Building a case like that was truly impressive and the answers my family received is closure,” Beyer said.

This is the fifth time the homicide unit has used investigative genetic genealogy to solve a cold case. The four other instances include solving the cases of Orbin Holloway, Teresa Solecki, Michelle Louise Wyatt and Laurie Dianne Potter.

Wyatt, who was 20 when she was found dead in 1980 by a roommate in Santee, was the most recent solved case prior to Wednesday’s announcement. As with Dahn’s case, Wyatt’s suspected killer died without ever being publicly identified as a suspect in her murder.

Authorities identified Potter — found in the dumpster of a Rancho San Diego apartment complex in 2003 — last year and arrested her husband Jack Dennis Potter on suspicion of the murder. He denies the charges.