The man suspected in the Golden State Killer crimes has been charged with four more murders, as authorities across California continue to piece together clues in a string of killings and rapes that terrorized the state four decades ago.Joseph James DeAngelo, 72, is facing four counts of first-degree murder in the separate killings of two couples in Santa Barbara County in 1979 and 1981, bringing the total number of slayings in which he has been charged to 12. DeAngelo, a former police officer and retired mechanic, also is suspected in more than 50 rapes.Santa Barbara County District Attorney Joyce Dudley said authorities never gave up hope that they would solve the killings of Robert Offerman and Debra Alexandria Manning, and Greg Sanchez and Cheri Domingo, when she announced the charges Thursday."Violent cold cases never grow cold for victims or their loved ones," Dudley said. "Most of them spend their lives feverishly seeking answers and desperately hoping for justice."Authorities arrested DeAngelo last month, after using a combination of DNA, genealogy and exhaustive detective work to conclude that the man quietly living out his golden years in a Sacramento suburb could be one of the nationís most notorious serial predators. It was a dramatic turn for a case that had long ago gone cold.DeAngelo was charged with two slayings in Sacramento County, two in Ventura County and four in Orange County. He is being held in a Sacramento jail and has not entered a plea in any of the cases. His attorney did not respond to a request for comment Friday.In the new charges, DeAngelo is accused of breaking into Offerman and Manningís Goleta, California, home shortly after Christmas in 1979. Media reports from the time said the couple was bound and shot. Manning also was raped.Authorities say DeAngelo struck about a half-mile away in July 1981, at the home of Sanchez and Domingo. The attacker tied up Domingo, then raped and killed her. Sanchez is believed to have fought the man before he was brutally bludgeoned to death.DeAngelo has now been charged in all the known slayings linked to the Golden State Killer, but police also are exploring whether he might have carried out the killings of a mother and son in the Simi Valley area in 1978. A man convicted of the murders was exonerated last year after serving nearly 40 years in prison.Police and prosecutors say the Golden State Killer - also known as the Visalia Ransacker, the East Area Rapist and the Original Nightstalker - began his crimes with a series of break-ins that escalated to brutal rapes in the Sacramento area in 1976. In 1979, the crimes migrated to Southern California, where DeAngelo is charged with carrying out a string of killings. The crimes appear to have ended in 1986.Investigators cracked the case by feeding the killerís DNA into GEDmatch, a genealogy database, which linked the DNA to distant relatives. Investigators then found a common set of great-great-great-grandparents shared by the killer and the relatives and traced their descendants to the present day.Detectives scoured the list of descendants for people who were within the right age range and had connections to the areas in California where the killings occurred. This led detectives to DeAngelo, who had never been a suspect.The technique has stirred concerns about the privacy of data submitted to genealogy sites, but it also has spurred a fresh effort to catch one of the nationís most infamous serial criminals, the Zodiac Killer.Police are hoping to find traces of the killerís DNA on letters he sent and then use the same technique employed in the Golden State Killer case to find a suspect.