We'll begin with that huge break in a cold case terrorizing California for decades. Police say they now have the golden state killer in custody. And they used DNA testing to find him. So many families are relieved this morning. The killer accused of murdering at least 12 people, sexually assaulting more than 50. 72-year-old Joseph James Deangelo hiding in plain sight in suburban Sacramento. ABC's whit Johnson is there with new details on the stunning break. Good morning, whit. Reporter: George, good morning to you. Absolute shock in this quiet community that the man who terrorized California may have been living right here, the golden state killer vanished in the '80s, gone for decades until investigators say a key piece of DNA evidence connected the dots just days ago. The 40-year manhunt for one of the most prolific serial killers perhaps coming to an end at this suburban home. We found the needle in the haystack and it was right here in Sacramento. Reporter: Police say this man, 72-year-old Joseph James Deangelo is the elusive golden state killer. The former police officer allegedly responsible for at least 12 murders, upwards of 50 rapes enmore than 100 burglaries in California from 1976 to 1986. Deangelo's name never coming up in prior investigations, but just six days ago, a critical clue. We started some surveillance. We were able to get some discarded DNA and we were able to confirm what we thought we already knew, that we had our man. Reporter: Deangelo, seemingly hiding in plain sight, police surprising him and taking him into custody on Tuesday as he was leaving his home. For the 51 ladies who were brutally raped in this crime scene, sleep better tonight. He isn't coming through the window. He's now in jail. And he's history. Thank you. Reporter: Deangelo's arrest bringing relief to victims and their families. I woke up to a text from a very good friend of mine who said do you think this is the guy and had an article attached saying they had somebody, they had made an arrest and I just started shaking. I never in my lifetime expected to see that. Reporter: Authorities say he worked as an officer at two different police departments until he was reportedly fired in 1979 for shoplifting dog repellant and a hammer. Very possibly he was committing the crimes during the time he was employed as a peace officer. Reporter: Also known as the original night stalker and east area rapist the killer taunted police. You're never gonna catch me. Reporter: And his victims with phone calls long after the attacks. Gonna kill you. Gonna kill you. Reporter: Leaving the entire state on edge. A significant development came in the mid '90s, DNA testing connecting the puzzle pieces to one unknown person. Crime writer Michelle Mcnamara who coined the phrase the golden state killer made it her life's work to hunt him down. She discussed the serial killer in an interview with filmmaker Cameron Cloutier. I'm struck by people did not call out there was a weird guy hanging around so he to fit in. But on the other hand it's just the level of violence is so extreme. Reporter: Mcnamara died in 2016. But with the help of her researchers and husband, comedian Patton Oswalt her book "I'll be gone in the dark" was completed and released in February. It debuted at number one on "The New York Times" best-seller's list sparking national interest in the case. You did it, Michelle. Even though the cops will never say it but your book helped get this thing closed. Reporter: And charges against Deangelo continue to pile up. Prosecutors believe that key piece of DNA evidence will link him to perhaps dozens of crimes spanning ten counties, they're promising more charges in the coming days. Robin. We'll talk more about that, whit, with Sacramento district attorney Anne Marie Schubert who joins us live this morning. What a relief. So many people relieved waking up this morning and we know that this case has been cold for decades and Deangelo's name didn't even surface until just six days ago. Is that right? That's correct. That's correct. And the discarded DNA didn't come from a tip from -- coming into your office so tell us more about the discarded DNA and how that was the key. Well, as we said yesterday, this case was really solved through some innovative DNA techniques so as a result of that, that led to law enforcement essentially as the sheriff said yesterday surveilling him and obtaining a sample of abandoned or discarded DNA and from there we moved forward and they did additional testing and that's what solved the case. My goodness. We know that he was once married. He was a police officer absentee ballots, an officer at the time of the crimes. When you look at grown children, how does he fit the profile that investigators are working with at the time? Well, he was never on a list so now we're at a point now as I said yesterday this is like lightning speed so everything is now trying -- is an active investigation but I think all those answers are going to be filled in over time, though. It is an active investigation and we appreciate you sharing as much as you are and we heard in the report as right now he's been charged with the first two known killings in the so-called golden state killing. How many more do you suspect and we know that the last killing was in 1986 but will he possibly look to -- for other cases since that time? Yeah, they'll absolutely look for additional cases. What we know now he is responsible for at least 12, perhaps 13. I'm fully confident he will be charged with an additional count of murder because he's linked to several other murders including in Orange county and Santa Barbara county. Ma'am, what do you want to say to people about the work that went into this and even though it was decades old that your office and everyone was not going to let this go unsolved? Well, it's all about passion and persistence and ultimately about DNA and I've always believed that DNA is a silent witness to the truth and that truth may have been quieted for 40 something years but beer's now here and have the answer. We appreciate your work very much. Anne Marie Schubert, thank you so much.