The El Dorado County District Attorney's Office said in a news release that Joseph Holt, a former real estate agent, was behind the killings of 27-year-old Brynn Rainey in 1977 and 16-year-old Carol Andersen in 1979.
"Joseph Holt was never on the radar," John Gaines, an investigator with the El Dorado County District Attorney's Office, told FOX40.
Brynn Rainey was working at a casino when she was reported missing in 1977. The 27-year-old's body was found about a month later in a shallow grave near Stateline Stables in South Lake Tahoe in August of 1977.
"She had been also sexually assaulted and appears to have been strangled as well," Gaines said.
Almost two years later, Carol Anderson was last seen alive while leaving a party. The 16-year-old's "battered body" was found on the side of the road, also in South Lake Tahoe.
"It was a July Fourth weekend in 1979. Her body was discovered the next morning, early morning hours," Gaines told FOX40.
Both murders had gone unsolved for decades until the El Dorado Cold Case Task Force employed Parabon Nanolabs to construct a “family tree” from DNA recovered from a blood stain on Brynn Rainey’s shirt and DNA recovered from Carol Andersen’s body during her autopsy.
In 2018, detectives across the country said they were able to locate suspects in 28 cold cases after uploading crime scene DNA to GEDmatch.com, a public genealogy website.
The website GEDmatch uses data from people who expressly grant consent for law enforcement before submitting, according to officials.
"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," California State University, Sacramento professor and forensic DNA expert Ruth Ballard told FOX40.
In El Dorado County, investigators used the recovered DNA that eventually led them to three deceased brothers who might be the source of the DNA recovered from the twin crime scenes.
After the task force collected DNA from a child of one of the brothers, in addition to DNA from a toothbrush that belonged to that brother, further testing confirmed that Joseph Holt’s DNA is a match to what was found on Brynn Rainey’s shirt and Carol Andersen’s body, experts said.
Holt, originally from San Jose, graduated from the University of California, Berkeley, he worked in real estate in South Lake Tahoe before dying of a heart attack in 2014. He was only identified as a suspect in 2018.
"Holt’s surviving family members had no idea he was a killer, and fully cooperated with law enforcement during this investigation," officials said.
The families of Brynn Rainey and Carol Andersen said they were "grateful to finally know who took their loved one so many years ago," officials said.
"They expressed their support for the use of this technology to solve crimes," the DA's office said.
Investigators in El Dorado County believe that Holt is responsible for other unsolved crimes. The task force is asking anyone who may have information concerning Joseph Holt, or any information concerning any unsolved crime in El Dorado County, please contact their tip line at 530-621-4590.
Fox News' Robert Gearty contributed to this report.