LOS ANGELES — A retired police officer who investigators believe is the "Golden State Killer," who terrorized California during the 1970s and the 1980s, was charged Thursday with four more counts of murder, bringing to 12 the number of slayings he is charged with.

"Violent cold cases never grow cold for their victims or loved ones," Santa Barbara County District Attorney Joyce Dudley said at a news conference to announce the charges of first-degree murder against Joseph James DeAngelo, 72, who was a police officer in the California towns of Exeter and Auburn during the 1970s.

DeAngelo was arrested April 24 at his home in the Citrus Heights suburb of Sacramento. He has also been charged with four killings in Orange County, two in Ventura County and two in Sacramento County, and he is scheduled to appear in court in Sacramento on Monday.

Until Thursday, however, he hadn't been charged in Santa Barbara County, where authorities believe he killed Robert Offerman and Alexandria Manning in December 1979 and Cheri Domingo and Gregory Sanchez in July 1981, Dudley said. Each of the four new counts of first-degree murder with special circumstances carries a possible sentence of death or life in prison without parole.

Dudley said all of the 12 charges were coordinated with her colleagues in the other counties, a process she called "unprecedented." She offered no further details.

From Sacramento south to the Los Angeles suburbs, the masked gunman raped women who were home alone and women who were with their children, and he killed women and men together, police have said.

Investigators have said they zeroed in on DeAngelo after scouring dozens of family trees on genealogy websites for possible DNA and profile matches. Critics of the investigative approach contend that it could jeopardize privacy rights.

Paul Holes, a retired investigator with the Contra Costa County district attorney's office who was closely linked to the case, said last month that investigators believed that DeAngelo, if he is the killer, was driven by the breakup of his engagement to a woman during the 1960s.

Holes — who retired less than a month before DeAngelo was arrested — said that when investigators began looking into his background, they found a newspaper article from the 1960s about DeAngelo's engagement to a woman whom he ended up not marrying.

"We assumed that there had been some breakup in their relationship and that possibly caused him some angst," said Holes, who described the Golden State Killer as "an anger retaliatory offender."

The killings stopped during the 1980s, but in 2016, the FBI offered a $50,000 reward for information leading to the killer's arrest.

The search took on renewed urgency in February with the publication of "I'll Be Gone in the Dark," a book about the case written by Michelle McNamara, the late wife of the comedian and actor Patton Oswalt. Oswalt helped to finish the manuscript after McNamara died in 2016.

Over the objection of several news organizations, lawyers for DeAngelo have asked a judge to seal arrest and search warrant records in the case, arguing that intense public interest could jeopardize his right to a fair trial.

Dudley stressed that DeAngelo is presumed innocent pending trial, but she added: "Justice delayed is justice denied. This has been a very long process for the victims."