Transcript for 'Golden State Killer's' spree allegedly began when he was a cop: Part 4
sledgehammer. They are caught easily. But every so often a blue moon surfaces. A snow leopard slinks by. The reason he evaded capture for so long is he's so evidence savvy. After an hour half it's over. It was like he knew every step that law enforcement was doing. In my estimation he's the most prolific major crime perpetrator, maybe in American history. Fwl police say they have the golden state killer in custody. Reporter: It is April 25th, 2018 -- almost 42-years after the golden state killer commits his first crime when, finally, a break in the case drops like a bombshell. It's unbelievable. After all these years, they got him. An arrest. Reporter: The man accused of being one of the most violent serial criminals in American history found hiding in plane sight. 72-year-old Joseph James Deangelo. I was shaking everywhere. The adrenaline just flooded. Reporter: The Vietnam war veteran discovered living in this sleepy Sacramento suburb. Living just a few hours away from you? Can you say the balls involved in being right here under all of our noses? He's been right here the whole time, living his life? Reporter: Authorities say Deangelo was tinkering on a woodworking project in his garage when investigators took him in to custody. The only thing he really said was that he had a roast in the oven. Reporter: Joe Deangelo appeared to live a quiet and Normal life. Working 27 years at this grocery distribution center fixing trucks, before retiring last year. He was married to a local attorney. The couple raising three daughters before reportedly separating in 1991. Were you surprised to learn that Joseph Deangelo is a father, a grandfather, family man? I wasn't. Because I had predicted that he would likely be blending in. Reporter: It was a different story for his neighbors, who say the man who kept a meticulous front lawn also had an explosive temper. He would go into a yelling tirade. Not sure who he was yelling at. A lot of four letter curse words. He'd accuse us kids here of spying on him in the backyard. He was paranoid at times. Reporter: Grant Gorman, who lived in the house directly behind Deangelo's says his neighbor once left his family an anonymous but threatening voice mail. It said, "If you don't shut that dog up, I'll deliver a load of death." Reporter: Perhaps the most alarming of revelations that Deangelo, at one point, had actually been a police officer. In 1973, he was working at this small police department in exeter, California. Well, I don't think anybody really got to know the guy. Reporter: Farrel ward says he worked patrol with Deangelo for three years. And I told him, he was overeducated. So why would you wanna stay in exeter? He should be in the FBI. Reporter: It was while he was a police officer authorities allege Deangelo's reign of terror begins. Now that we identified and he was a law enforcement officer, yeah, he understands all this and he's using it to his advantage. Reporter: Deangelo would then move north -- working, here, at the Auburn police department outside Sacramento. He had a nickname on the department. It was "Junk food Joey." Junk food Joey? What was that about? He would have a coke in his hand, a bag of chips or candy bar. Reporter: At times, Deangelo's behavior made his colleagues uncomfortable. When he'd talk to you, he'd get close to your face and always be touching you. He was very touchy? Yes. I remember one time I told him, "You know, Joe, my mother doesn't touch me as much as you do." You know -- How did he respond to that? Oh, he -- he got his feelings hurt. Reporter: Willick fired Deangelo in 1979 for stealing dog repellent and a hammer from a local hardware store, saying Deangelo later filed a lawsuit against the department. The investigator told me that Joseph had gone to my house one night to kill me. And said that he walked around the house lookin' in the windows but couldn't find my bedroom. And when you heard that you thought what? I just never saw him as a person who could, you know, kill somebody. Reporter: But Willick says looking back he now remembers something else. A short time after he had been fired, I woke up one morning, my 4-year-old daughter was laying alongside the bed. She said, "Dad, last night there was someone lookin' in my bedroom window with a flashlight." Did you think that could have been Joseph Deangelo outside your home? No, I did not. I did not. Reporter: There is one more chilling detail that helped investigators target their suspect. Remember that mysterious name, Bonnie. The name one woman told authorities her rapist called. Could that hold a clue? You thought this guy had a grudge? He had a grudge. And we didn't know was Bonnie his mom, a wife, ex-wife, girlfriend? We just knew that there was a Bonnie in his life. Tell me how Bonnie's name helped you zero in on Joseph Deangelo. When we're looking at Joe Deangelo, we run across a newspaper article of an engagement to a Bonnie back in 1970. So, now we have a guy that has a Bonnie in his life. And we couldn't find any indication that they ever got married.
This transcript has been automatically generated and may not be 100% accurate.