It was a Monday afternoon in 1988 when a co-worker found 29-year-old Diane Lynn Dahn bludgeoned and stabbed to death in her apartment in Santee. Wandering nearby was Dahn’s 2-year-old son.

The case went unsolved for 34 years.

Now, Dahn’s son, Mark Beyer, 36, says he finally has closure.

On Wednesday, sheriff’s officials announced they had a suspect. They used DNA and a process known as genetic genealogy to identify the accused killer: Warren Robertson.

Robertson died in a house fire in Indiana in 1999. He was 39.

“The answers that my family received — it’s closure, and closure is everything, even after so much time had passed,” Beyer said in a video officials showed during a news conference.

According to investigators, Robertson and Dahn lived in the same apartment complex on Graves Avenue near Prospect Avenue in 1988. Robertson was a tow truck driver; Dahn worked as an electronics technician with San Diego Transit Corp. Both were racing enthusiasts who attended stock car races.

Investigators were unable to determine if they knew each other before the slaying.

Also unknown is the motive. Although Dahn was nude when her body was found, investigators said there was no evidence of sexual assault. They said Robertson…