We have a development in the case of the former police officer under west. Officials believe he committed more than 12 murders and 40 rapes. Tonight, they reveal how they caught him all the years later. And the audio. You will hear the phone messages he could leave his victims after the attacks. Tonight is Tim Johnson. Reporter: Tonight, investigators building their case against the suspected golden state killer -- searching the home of 72-year-old Joseph James Deangelo for items stolen from the victims. We may be able to connect some of the burglaries that are really just linked to him based upon Mo and no DNA so that we can link some of those cases to him moving forward. Reporter: And we're learning more about how the alleged predator was captured. After trailing Deangelo for six days, more than 15 officers watched as he worked inside his garage. Then moving in, when he walked out to the sidewalk. Dangelo, who was home alone, appeared surprised. Really no conversation at all. Just the only thing he really said was that he had a roast in the oven. Reporter: Tonight some neighbors saying the man now accused murdering 12 people and raping nearly 50 victims lived with family and had a temper. We used to call him freak because he used to have these tantrums out in the front. He would yell so loud that you could hear him yelling from inside the house. Reporter: Grant Gorman claims he had multiple run-ins with Deangelo. Including a threatening call over his barking dog. If you don't shut that dog up, I will deliver a load of death. Reporter: Deangelo recently retired from his job at this save mart grocery distribution center. As a young man, he served in the Navy. And while some of the early crimes were being committed. Deangelo was a police officer, reportedly fired in 1979 for shoplifting dog repellant and a hammer. The golden state killer known for taunting his victims. He asked me in a very harsh whisper do you want to die do you want me to kill your mother. Reporter: Margaret Wardlow believed to be the youngest just 13 at the time. Her attacker tying up her mother like he did others, stacking plates on her back to make sure she wouldn't move. Just awful. With us, we know after 40 years on the run, new DNA technology helped track down Deangelo. You are just learned, what turned the case? Reporter: Yeah, David, we just learned from multiple law enforcement sources that investigators used genealogy websites to link Deangelo to the unknown DNA of the attacker. It provided a critical clue in the case.