PLACERVILLE -- Answers are surfacing four decades after two brutal killings in South Lake Tahoe.
Carol Andersen was only 16 when she was found dead. The Zephyr Cove high school student was last seen leaving a party.
"It was a July Fourth weekend in 1979. Her body was discovered the next morning, early morning hours," said John Gaines, an investigator with the El Dorado County District Attorney's Office.
Brynn Rainey worked at a casino. Investigators say in the summer of 1977 the 27-year-old's body was found in a shallow grave.
"She had been also sexually assaulted and appears to have been strangled as well," Gaines said.
El Dorado County DA Vern Pierson said their two families were "frozen in time," suffering for years with no arrests, no suspects and no information -- until now.
"It wouldn't have happened without this technology," Gaines said.
The El Dorado County Cold Case Task Force identified suspect Joseph Holt with the help of genetic genealogy, the same type of technology used in the Golden State Killer case.
"I'm excited for the forensics community to have this new tool and to have cases solved that probably would never have been solved otherwise," said California State University, Sacramento professor and forensic DNA expert Dr. Ruth Ballard.
Ballard said these difficult cold cases are getting solved because of the growth and popularity of public DNA databases, like GEDmatch, which law enforcement agencies can access without court orders.
"The bigger and more expanded these public databases become the easier it's going to be to identify suspects more quickly and solve crimes more quickly," Ballard told FOX40.
In El Dorado County, investigators had preserved DNA from a blood stain and one of the victims' bodies.
Using the database, a family tree and more testing, Holt was identified.
"Joseph Holt was never on the radar," Gaines explained.
He went undetected his whole life.
Investigators say Holt was from San Jose. A graduate of the University of California, Berkeley, he worked in real estate in South Lake Tahoe before dying of heart attack in 2014.
But for two families, the decades-long mystery is over. The DA's office says the family members of the victims are grateful to finally know who killed their loved ones.
Holt's family cooperated with the investigation and provided more DNA to help investigators confirm the match.
El Dorado County investigators believe Holt is responsible for more crimes. Their task force asks anyone with information to call their tip line, 530-621-4590.