When the investigators first questioned one early victim of the Golden State Killer in Davis, California, they weren't sure the woman had correctly heard what the assailant had sobbed as he raped her in the late 1970s.

"The original investigator asked her, 'Are you sure he isn't saying Mommy?'" Paul Holes, a retired Contra Costa County District Attorney's Office investigator closely linked to the investigation, told NBC News.

Bu the victim was adamant — the man who sexually assaulted her kept saying "I hate you, Bonnie," over and over again.

Officials now say that the man believed to be the Golden State Killer, Joseph James DeAngelo, might have been motivated in part by lost love to commit a lengthy string of rapes and murders through the 1970s and 1980s.

"We always thought that our offender had a Bonnie that was significant in his life, either a mother, a wife, an ex-wife, a girlfriend," Holes said. "We don't know, but that was something that we would look for when we were evaluating potential suspects."

DeAngelo, a 72-year-old former police officer, was arrested last week in Sacramento after DNA evidence helped police connect him to the decades old murders and rapes.

17 PHOTOS Golden State Killer case See Gallery Golden State Killer case Joseph James DeAngelo, 72, who authorities said was identified by DNA evidence as the serial predator dubbed the Golden State Killer, appears at his arraignment in California Superior court in Sacramento, California, U.S., April 27, 2018. REUTERS/Fred Greaves An investigator puts evidence bags in a sheriff's vehicle after removing them from the home of Joseph James Deangelo, who was arrested for the East Area Rapist/Original Night Stalker/Golden State Killer case in Citrus Heights, California, U.S., April 26, 2018. REUTERS/Fred Greaves Melanie Barbeaux holds a photo of victims of the Golden State Killer in the courtroom as Joseph James DeAngelo, who authorities said was identified by DNA evidence as the serial predator dubbed the Golden State Killer, appears at his arraignment in California Superior court in Sacramento, California, U.S., April 27, 2018. Sacramento Bee/Randy Pench/Pool via REUTERS A combination image shows FBI sketches of an unknown individual known as the East Area Rapist/Golden State Killer (EAR/GSK) described as a White male, currently thought to be between the ages of 60 and 75 years old, shown in sketches released on June 15, 2016. Between 1976 and 1986, this individual was responsible for approximately 45 rapes, 12 homicides, and multiple residential burglaries throughout the State of California. FBI/Handout via REUTERS ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY. EDITORIAL USE ONLY An unknown individual known as the East Area Rapist/Golden State Killer described as a White male, currently thought to be between the ages of 60 and 75 years old, is shown in this FBI sketch released on June 15, 2016. Between 1976 and 1986, this individual was responsible for approximately 45 rapes, 12 homicides, and multiple residential burglaries throughout the State of California. FBI/Handout via REUTERS ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY. EDITORIAL USE ONLY An investigator removes items in evidence bags from the home of Joseph James Deangelo, who was arrested for the East Area Rapist/Original Night Stalker/Golden State Killer case in Citrus Heights, California, U.S., April 26, 2018. REUTERS/Fred Greaves Sheriff's crime scene tape surrounds the house belonging to Joseph James Deangelo, who was arrested for the East Area Rapist/Original Night Stalker/Golden State Killer case in Citrus Heights, California, U.S., April 25, 2018. REUTERS/Fred Greaves An unknown individual known as the East Area Rapist/Golden State Killer described as a White male, currently thought to be between the ages of 60 and 75 years old, is shown in this FBI sketch released on June 15, 2016. Between 1976 and 1986, this individual was responsible for approximately 45 rapes, 12 homicides, and multiple residential burglaries throughout the State of California. FBI/Handout via REUTERS ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY. EDITORIAL USE ONLY A police officer removes items in evidence bags from the home of Joseph James Deangelo, who was arrested for the East Area Rapist/Original Night Stalker/Golden State Killer case in Citrus Heights, California, U.S., April 26, 2018. REUTERS/Fred Greaves Sheriff's crime scene tape surrounds the house belonging to Joseph James Deangelo, who was arrested for the East Area Rapist/Original Night Stalker/Golden State Killer case in Citrus Heights, California, U.S., April 25, 2018. REUTERS/Fred Greaves Sacramento Sheriff Scott Jones talks about the arrest of a suspect in the East Area Rapist/Original Night Stalker/Golden State Killer case in Sacramento, California, U.S., April 25, 2018. Jones along with Sacramento District Attorney Anne Marie Schubert, law enforcement leaders, the FBI and other elected District Attorneys from several other California counties participated in the news conference announcing the arrest of Joseph James Deangelo. REUTERS/Fred Greaves An FBI evidence response team member walks into the garage of Joseph James Deangelo where other investigators were looking for evidence after Deangelo was arrested for the East Area Rapist/Original Night Stalker/Golden State Killer case in Citrus Heights, California, U.S., April 25, 2018. REUTERS/Fred Greaves An unknown individual known as the East Area Rapist/Golden State Killer described as a White male, currently thought to be between the ages of 60 and 75 years old, is shown in this FBI sketch released on June 15, 2016. Between 1976 and 1986, this individual was responsible for approximately 45 rapes, 12 homicides, and multiple residential burglaries throughout the State of California. FBI/Handout via REUTERS ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY. EDITORIAL USE ONLY SACRAMENTO, CA - APRIL 27: Joseph James DeAngelo, the suspected 'Golden State Killer', appears in court for his arraignment on April 27, 2018 in Sacramento, California. DeAngelo, a 72-year-old former police officer, is believed to be the East Area Rapist who killed at least 12 people, raped over 45 women and burglarized hundreds of homes throughout California in the 1970s and 1980s. (Photo by Justin Sullivan/Getty Images) Joseph James DeAngelo is taken on a wheel chair into the courtroom to be arraigned on two counts of murder April 27, 2018, in Sacramento, California. I - Investigators have accused him of of being the 'Golden State Killer,' who is suspected of committing more than 50 rapes and 12 murders. (Photo by Elijah Nouvelage / AFP) (Photo credit should read ELIJAH NOUVELAGE/AFP/Getty Images) SACRAMENTO, CA - APRIL 27: Joseph James DeAngelo, (L) the suspected 'Golden State Killer', appears in court for his arraignment before Judge Michael Sweet (R), on April 27, 2018 in Sacramento, California. DeAngelo, a 72-year-old former police officer, is believed to be the East Area Rapist who killed at least 12 people, raped over 45 women and burglarized hundreds of homes throughout California in the 1970s and 1980s. (Photo by Justin Sullivan/Getty Images) Up Next See Gallery Discover More Like This HIDE CAPTION SHOW CAPTION of SEE ALL BACK TO SLIDE

Holes said when investigators began looking into DeAngelo's background, they found a newspaper article from the 1960s about his engagement to a woman named Bonnie Colwell. The engagement never produced a marriage, however.

"So we assumed that there had been some breakup in their relationship and that possibly caused him some angst," Holes said.

NBC News was not able to contact Colwell, but NBC Sacramento affiliate KCRA spoke with her daughter, who said her mother plans to speak with the Sacramento County District Attorney.

DeAngelo eventually married another woman, Sharon Huddle, in 1973, according to the Ventura County Star. The couple has been estranged since the mid-1990s, according to the newspaper.

Holes said he doesn't believe DeAngelo is mentally ill, but instead classified him as "an anger retaliatory offender."

"This is an individual that [has] stressers in his life, people in his normal life make him angry and when that happens, he ends up taking his anger out on victims, ... and the instance where he is saying 'I hate you Bonnie, I hate you Bonnie,' — obviously, Bonnie is making him upset at that moment in time," Holes said.

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