With the filing of the charges, DeAngelo is now charged with all 12 of the murders attributed to the Golden State Killer.
He is facing charges for two killings in Ventura County and two in Sacramento County.
Last week's arrest of a suspect in the Golden State Killer case in California has highlighted how DNA samples that have been volunteered for one objective - in this case, genealogy - can be used for other reasons, often without the donor's explicit consent.
He was arrested last month and remains jailed in Sacramento County. "Each of the four counts carry the potential for life without the possibility of parole or the death sentence".
Joseph James DeAngelo, 72, is believed to be linked to several homicides in the Santa Barbara area in the late 1970s and early 1980s.
Californians lived in fear that the Golden State Killer-also called the Cordova Cat Burglar, the Visalia Ransacker, the East Area Rapist, and the Original Night Stalker-was still out there all these years later.
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He was initially charged with eight counts of murder, but have four more added to his docket this week.
Prosecutors say DeAngelo, a former police officer, was one of California's most elusive serial killers.
DeAngelo is charged with the murders of Dr. Robert Offerman, 44, and Dr. Debra Alexandra Manning, 35, who were found shot dead at Offerman's condominium on Avenida Pequena in Goleta on December 30, 1979. They got lucky: a match with family members led them to identify and arrest Joseph James DeAngelo.
"Violent cold cases never grow cold for victims or their loved ones", Dudley said.
"The sense of relief is overwhelming and it's wonderful", Debbi Domingo, daughter of Cheri Domingo, told Noozhawk.com, a Santa Barbara County news website.
Amy Lieu is a news editor and reporter for Fox News.