On Wednesday, police arrested a suspect they believe is behind a series of unsolved killings, rapes and assaults in the 1970s and 1980s, including the deaths of Harrington's family members.
Joseph James DeAngelo was charged with capital murder in the 1978 killing of Katie and Brian Maggiore. The 72-year-old former police officer is believed to be linked to 12 killings and at least 50 rapes in California, police said.
Harrington and dozens of survivors had only known the mysterious killer as "the Original Night Stalker," "East Area Rapist," and the "Golden State Killer."
"Sleep better tonight. He isn't coming through the window," Harrington addressed survivors at a news conference Wednesday. "He's now in jail and he's history."
DeAngelo's arrest brought a mix of emotions to survivors and the victims' families.
"There are a million and one things going through my mind. It's really quite overwhelming," Debbi Domingo told HLN's Ashleigh Banfield.
Domingo was a teenager when her mother Cheri was killed in 1981 at their Goleta, California, home. In recent years, she had become active online and posted YouTube videos calling for answers in her mother's case.
After Domingo heard that someone was in custody, she said she felt "a wave of relief."
'We just didn't talk about rape back then'
Jane Carson-Sandler was dozing in bed with her son when she was abruptly awoken by a masked man holding a butcher knife in 1976.
The man bound and blindfolded them before he moved her son to another room. Then, he came back to rape her, she told HLN's Michaela Pereira.
That first rape sparked the hunt for the so-called Golden State Killer but Carson-Sandler believes there could be more that may have not been reported to police.
"I think what we didn't have back at that time was the ability to share what happened to us because of shame," she said. "We just didn't talk about rape back then."
"It's so different today and I just really, I just hope some of those other women that were raped by him can finally, maybe come forward," she added.
Embracing the 'power of DNA'
Harrington praised law enforcement after they revealed they had matched a discarded DNA sample from DeAngelo's home to evidence from the decades-long investigation.
At the press conference with police, Harrington said he had been lobbying to bring DNA testing to the forefront of forensic science in California for years.
"I began my quest in the mid 90s. It was 15 years until we heard that there was a DNA sample taken from our scene," he said at the press conference Wednesday.
In the early 2000s, he testified in front of the California Assembly in favor of expanding DNA collection by police and "pleading that they would embrace the power of DNA."
In 2004, California voters passed Proposition 69, an initiative to collect DNA from people arrested with felonies charges and store it in a state database.
"What's driving me is a sense of wanting to avenge the death of my brother and his wife," Harrington told the Los Angeles Times before the initiative was approved.
'You're gonna survive'
Margaret Wardlow was 13 years old when she was raped at her Sacramento home after a man woke her up with a flashlight to her face.
"My inside voice told me, 'You are going to be raped, this is what's going to happen to you, and you're going to live through this, you're gonna survive,' and it was just that simple," she told CNN affiliate KVOR.
She faced him with defiance, she said, even as he threatened to kill her mother.
"I just knew I wasn't gonna let him have what he came for, and that was to have power over me by frightening me and making me fear him," Wardlow said.
Wardlow believes her courage has got her through the years since the attack.
"It's never defined who I was or who I am today," she told CNN affiliate KSWB. "I've never let an evil person interfere with my life, how I want to live it and I am very proud to be able to say that."