The deadly crime spree of the "Golden State Killer" includes a five-year pause that has remained a baffling mystery to this day.
But now, with the arrest of 72-year-old Joseph James DeAngelo, a former police officer, the lead detective in the case believes he knows why the alleged serial killer who terrorized California residents for two decades took a break between a 1981 double homicide and the last slaying attributed to him in 1986.
Retired Det. Paul Holes, who investigated the case for decades, says in an interview to air Friday on ABC's "20/20" that he believes fear of being confronted by a combative victim caused him to halt the attacks after the murders of Cheri Domingo and Gregory Sanchez on July 27, 1981, in Goleta.
And Holes said lust is likely the reason the killer struck again on May 4, 1986, with the rape and murder of Janelle Lisa Cruz in Irvine.
"I believe what ended up happening were two things: In 1981, he ends up going into kill Gregory Sanchez and Cheri Domingo. And he gets in a physical fight with 6-foot-3 Gregory Sanchez. And I think that physical altercation with Sanchez scared him. We don't have an attack for five years," Holes said in the interview.
"But then ... for some reason, he runs across beautiful 19-year-old Janelle Cruz and can't help himself. And kills her," said Holes, a former Contra Costa County cold-case detective.
Following Cruz's killing, the "Golden State Killer" rampage suddenly stopped. No other cases were linked to the serial killer, and Holes shared his theory why he seemed to go into retirement.
"At this point, he's an aging offender," Holes said. "And so, he is no longer in that prime where he's now going out as frequently as he wants, naturally due to his age."
But Holes said "it is possible, but I think it's relatively unlikely" that the killer continued his reign of terror after he targeted Cruz.
"But I can't say for sure," Holes said. "I know we have looked over the years for additional cases, 'cause we wanted to try to see if we could find more. And we haven't. So, it's not just starting that search now. That's been ongoing for a long time. And we've been unsuccessful."
Detectives suspect that during the crime spree, the "Golden State Killer" committed 12 murders, at least 50 rapes and multiple home burglaries throughout the state. They believe he first struck on June 18, 1976, when, wearing a mask and gloves, he broke into a woman's home in Rancho Cordova and robbed her of money and jewelry.
DeAngelo worked as a police officer in the rural central California town of Exeter from 1973 to 1976, and later for the Auburn, California, Police Department until 1979, when he was fired for shoplifting dog repellent and a hammer, officials said.
At the start of the "Golden State Killer" crime spree, DeAngelo would have been 31 years old. At the time of Cruz's rape and murder, he would have been 40.
The Sacramento County Sheriff's Department, which is currently investigating the case, has not publicly offered any theories as to why the killings paused during the five years or stopped after 1986.
DeAngelo, a married father of three adult children, was arrested on April 24 at his home in Citrus Heights, a suburb of Sacramento, after detectives used DNA evidence allegedly linking him to the cold-case crime spree.
"Finally I got to see the face of the man that I've been hunting for 24 years," Holes said of DeAngelo's arrest. "I can now read these case files and visualize Joe DeAngelo committing these acts, as opposed to this nameless masked man."