"We all knew that we were looking for a needle in a haystack but we all knew that the needle was there", said Sacramento District Attorney Anne Marie Schubert.
Authorities declined to name the online site.
Contacted Friday, both Ancestry and 23andMe.com said they weren't involved in the case.
It's not the that of it that anyone has an issue with since the better part of ourselves always desires justice, it's the how - namely, the police use of a genealogy website GEDMatch to go from point A (the killer's DNA sample found at two murder scenes) to point B (a relative's match) to lead back to point A.
Chief Deputy District Attorney Steve Grippi said that the DNA used to zero in on DeAngelo had been uploaded by a relative, according to NBC affiliate KCRA. "He was going to show police that he was smarter than any of them and that it was a mistake to fire him". It's unregulated and there is no court order that is needed.
DNA potentially may have played an earlier role in the case.
Investigators then used the results to explore different family trees and find men who fit the profile of the Golden State Killer - roughly the right age and height, and who had been living in California when the crimes took place.
For Oswalt, the news of DeAngelo's arrest feels deeply personal. The Golden State Killer was linked to 12 murders, 45 rapes and more than 120 home burglaries that spanned from Northern California to Ventura and Orange counties.
Mr DeAngelo has initially been charged with eight counts of murder.
He has since posted a series of Tweets about the suspect and how certain aspects of his life seem to line up with alleged clues in the case.
McNamara seemingly foreshadowed the arrest in a chilling piece of writing, "letter to an old man" at the end of her book, which was released in February.
Emmy Award victor Oswalt earlier shared his thoughts in a video on Instagram about the arrest, which McNamara had been digging into from 2013 until her death.
But it was only over the last few days that information "started to point toward" DeAngelo, and police began investigating him, said Sacramento County Sheriff Scott Jones.
A retired policeman who previously worked with the man accused of being a serial killer and rapist said it's possible that suspect Joseph James DeAngelo helped with a search in a killing he's now suspected of committing.
DeAngelo had both. He served six years as a police officer after serving for almost two years in the Navy during the Vietnam War.
Ward doesn't recall DeAngelo directly working on the case.
But Michelle McNamara, by reaching millions of readers, shined a brighter light on this case than had ever been shone before. Authorities said other charges could be filed.
Huddle told The Associated Press it is "still just going insane in my mind". "I don't understand that". Today it was revealed that DeAngelo was a police officer in the towns of Exeter (just southeast of Visalia) and Auburn (northeast of Sacramento) between 1973 and 1979, but was sacked by Auburn's department after shoplifting a hammer and dog repellant from a drugstore.