Transcript for The New 20/20 Event Special airs Friday at 9|8c on ABC
What was it list might have toughest look at he was a phantom of the society. Here is he sophisticated. Sadistic killer. He was attacking people rear they feel the most safe in bed with their partner in their home every time investigators thought they were getting close. He would disappear. He murdered more people than the city killing has little name recognition. Returns and on post here. Michelle McNamara was he true crime blogger Mary pat Oz. Mom during the day writing it not true crime. The reason boxer house's. History pain is our eats. There's something seriously hurt it taxing taxing EDT me tell from law. Can't ever act. He was right their face move don't kill you he put plates on the man's if I hear the threat I will kill your life sometimes he would call. And talk. That he got personal censor people's lives. Just want story. Or this person she was on a relentless pursuit to find its kill. Forensic geology Michelle was excited Michelle definitely believed she itself this case a case that a lot of people solvable. Praising him. You're shaking up. I think it when we don't this is like the big important you can actually tell anybody about it and that apple. We just hear over the radio go. Only succession you know. Went for a serial killer help and Smart people and solve the unsolvable case the new 20/20. Special Friday noon central.
This transcript has been automatically generated and may not be 100% accurate.