CITRUS HEIGHTS, Sacramento County — Joseph James DeAngelo, the ex-cop and retired grandfather accused of terrorizing California with a series of rapes and killings — spurring a decades-long manhunt that ended this week — committed most of his murders in a spree that began three months after he was fired from his job as a police officer in Placer County, police said.

But as investigators in several counties build cases against DeAngelo, who was named as the notorious “Golden State Killer” and “East Area Rapist,” they’ve said little about a possible motive in crimes that spanned from 1976 to 1986.

They believe the 72-year-old Vietnam veteran — set to make his first court appearance Friday in Sacramento — crisscrossed the state, seemingly picking victims at random. They believe he left behind his terrible pastime to grow older in the quiet Sacramento suburbs, work at a Save Mart distribution center and raise a daughter and granddaughter.

DeAngelo was known among neighbors for bouts of anger, but they had no idea he could be linked to one of the nation’s worst unsolved crime cases.

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The arrest of Joseph DeAngelo in connection with the East Area Rapist and Golden State Killer cases.

Media: San Francisco Chronicle

James Reavis, a forensic psychologist in San Diego who has studied serial killers, said a firing can trigger rage in psychopaths who extend preexisting sexual sadism into homicidal violence. Rage killings can happen on occasion with normal people, he said, but “it wouldn’t go on and on and on unless there was something wrong internally.”

DeAngelo, arrested early Wednesday at his home, is scheduled to appear in a Sacramento County courtroom Friday to face two murder charges. He’s accused of shooting to death a young couple near their Rancho Cordova home in 1978 as they walked their dog.

DeAngelo is expected to face a litany of criminal counts filed by prosecutors across the state. Investigators say they’ve connected him through DNA to a 12 slayings and 45 rapes. Two sources told The Chronicle that detectives tracked down DeAngelo by running crime-scene DNA against consumer genealogical websites, giving them possible relatives of the target, then building a pool and narrowing from there.

The district attorney’s offices in Ventura County and Orange County announced Thursday that they also would be filing murder, rape, robbery and other charges in at least six other killings. In some counties, prosecutors said they may not be able to file rape charges because the statute of limitations has passed.

As prosecutors made their decisions, a chilling picture emerged of a sadistic killer.

DeAngelo allegedly committed rapes while he worked as a police officer in Auburn, in Placer County, starting in 1976. He was fired from the Auburn force in 1979 after he was charged with stealing a hammer and dog repellent from a drugstore, officials said.

Detectives said the third murder attributed to the Golden State Killer was committed in Santa Barbara County on Oct. 1, 1979, three months after DeAngelo was fired. As the spree went on, it saw chilling behavior from the man also known as the “Diamond Knot Killer” and the “Original Night Stalker.”

The assailant allegedly cried, “I hate you, Bonnie. I hate you,” as he raped one of his victims. DeAngelo was briefly engaged to a woman named Bonnie Jean Colwell when he was 24, according to a book on the case written by Richard Shelby.

The killer was known to stake out his victims and break into homes to case the place before the carefully planned assaults, which usually occurred at night. A couple who once questioned the existence of the rapist at a town hall meeting became victims of the rapist, who was apparently listening, the Sacramento Bee reported.

He often placed dinner plates on the male victims and told couples he would kill them both if he heard the plates fall while he was raping the woman, investigators said.

“That is just classic psychopathy,” Reavis said. “In the moment, he is the evil genius, omniscient, omnipotent and he holds this person’s life in his hands. My guess is that would be incredibly exciting to him and also sexually arousing. It’s classic predatory aggression.”

According to investigators, DeAngelo took a five-year break from preying on victims after his daughter was born in 1981, and then, after a rape and murder in Orange County in 1986, apparently stopped altogether.

He appears to have been living a relatively normal life at the time of his arrest. He was retired and living in the Citrus Heights suburbs of Sacramento after working at a Save Mart distribution center for nearly three decades.

“Joe DeAngelo was a 27-year employee of the Roseville distribution center, having retired last year,” Victoria Castro, a spokeswoman for the company, said in a statement. “None of his actions in the workplace would have led us to suspect any connection to crimes being attributed to him.”

Reavis, like detectives, could not explain DeAngelo’s alleged pattern.

“When I read that he had stopped, I thought that he was probably incarcerated, but that doesn’t seem to be the case,” he said. “It could be the intensity of his sexual fantasies may have gone down with increasing age. You’d also have to consider whether there were more murders ... that we’re not aware of.”

Several rapes, but no murders, were committed in Danville, Walnut Creek, San Jose, Fremont and San Ramon in 1978 and 1979, police said. In addition to the homicides and rapes, authorities suspect DeAngelo committed more than 150 home break-ins across the state.

On Thursday, FBI investigators searched DeAngelo’s garage, along with a blue Volvo, white Toyota and silver fishing boat with the word “Klamath” painted in white letters on the side. Neighbors said he lived with a grown daughter and granddaughter.

They described the neighborhood as quiet, but said DeAngelo was loud.

“Joe kinda kept to himself. I knew his name was Joe but we used to always just call him ‘freak.’ His nickname was always ‘freak’ and now it’s really appropriate,” said Natalia Bedes-Correnti, 47, who has lived across from DeAngelo for 20 years.

DeAngelo was known for his loud voice and constant yelling, neighbors said.

“He used to yell and curse and curse and yell. He liked the f-word,” Bedes-Correnti said. “I just thought he was anger management grandpa.”

Sarah Ravani, Peter Fimrite and Sophie Haigney are San Francisco Chronicle staff writers. Email: sravani@sfchronicle.com, pfimrite@sfchronicle.com, sophie.haigney@sfchronicle.com