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When investigators first questioned a woman who had survived an attack by the Golden State Killer in Davis, California, they weren't sure she had correctly heard what her 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 investigator with the Contra Costa County district attorney's office who was closely linked to the case, told NBC News.

But 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 while committing a string of rapes and murders through the 1970s and ′80s.

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"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 attacks.

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 couple never married, 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," Holes said. "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."