Transcript for Deborah Roberts on her '20/20' special 'My Father BTK'
Dennis Rader is one of America's most infamous serial killers who brutally murdered 10 people while taunting the police with letters signed btk, short for bind, torture, kill. Tomorrow night on "20/20" Deborah Roberts sits down with the woman who only knew him as dad, until the day the FBI knocked on her door. Please welcome Deborah Roberts. So you sat down with his daughter Kerri. She talked about him as just her dad. That's how she grew up with him, as her dad. You heard her say he was a church president, a boy scout leader. He walked her down the aisle at her wedding, took her off to college. He was just an ordinary man in an ordinary midwest community and she finds this out at age 26, one year after she had gotten married. Her world was just like blown apart. What is it about this time because we were talking yesterday about Ted Bundy, so we were talking about Ted Bundy yesterday who was doing it around the same time, '70s and '80s. There were many serial killers floating -- was it something in the air? What the hell? It's kind of crazy. Golden state killer. In this case Dennis Rader was sort of affected by all of this stuff. He was fascinated in a very sick way. He admired Ted Bundy. He admired a lot of these other killers, the Boston strangler. He was just a very sick man masquerading as the guy next door, the last person police would ever think to look for. Wow. He was also doing this in Wichita, was it? Wichita. For how many years? Three decades, 30 years, before she was born. People are wondering, I'm wondering, how do you get away with that? No one knows? There were no red flags, nothing? When you think about it, obviously today we have so much more knowledge and there's forensics evidence and all of this but at that time they had very ruddmentry kinds of things that they were dealing with and also too he was just the guy at the grocery store, in the movies, at the church. A wolf in sheep's clothing. And then you asked the daughter about that exact question. We have a clip of that. Let's watch. Do you think your mom had any clue that your dad was doing anything criminal? No. Mom and I both said if we had had an inkling that my father had harmed anyone, let alone murdered anyone, let alone ten, we would have gone screaming out that door to the police station. We were living our Normal life. We looked like a Normal American family because we were a Normal family, and then everything upended on us. If his family had no idea what he was up to or even saw any evidence of this over 30 years, it really makes you question how well do you know anyone? Wow. So even now, looking back, sometimes hindsight is 20/20. Very nice, joy. So is there anything now that she can come up with? No because she was a child. In her book, "A serial killer's daughter" and whoop E, you said you're listening to it, she was a child. Who goes snooping around your parents' rooms. There was no reason other than he had a hair trigger temper. Didn't he try to strangle -- One time he snapped. He was upset. Now when she looks back she says there was a sort of amount of paranoia that he displayed sometimes. Now when she looks back she thinks maybe he was worried he was about to be caught. Not only did he hide from his family but the police as well for 30 years which is mind blowing to me, was finally arrested in 2005. How did they finally catch him? He played this game of cat and mouse. He would write letters. He would taunt them. Over years, maybe he stopped for a little while, then he'd do it again. His hubris caught up with him. He wanted to be known for all these killings so he sent a floppy disc to one of the TV stations just to show them a little test. What he didn't know was that it was encrypted at the church. It had some information from the church where he worked and they were able to actually trace it to the church and get some DNA evidence and eventually pin it on this man that nobody would have expected. Did he plead guilty right away? He pled guilty right away and confessed in a very dramatic fashion in the courtroom and on "20/20" you'll see just jaw-dropping testimony or just comments from him in court, almost blase' bragging about the victims. I remember he said I put them down, like putting down a dog. Or he felt sorry for them or he even offered a pillow to one of his victims because he knew that he had back problems. Very, very sick. But for Kerri this is very difficult because that's not the man she knew. She loved her father. Well, he is serving, I think, ten consecutive life sentences. He'll never see the light of day. Does she have any contact with him? Has she visited him? She has not visited him. But she has written him letters over the years and she has been in contact. She said that she would probably lose her mind if she just accepted that her father was a serial killer. She has to hold onto some of those memories of her happy childhood. She's compartmentalizing. She has to for her own kids. Two young kids. Knowing that her own dad killed two kids. And we're in a world of social media where one day they're going to be able to find out all of this which is why she says she wrote this book. Does she still love him? She says she loves her father. She loves the man who raised her, not the man that she learned about later on. She hopes that he can be forgiven. Does she worry about tendencies? That's a very good question and I asked her about that. She does not worry about that. I think she can't let her mind go there. She says I've never even had a traffic ticket. I've not the kind of person who's ever ever had in kind of problem so she doesn't think that's something for her to worry about or her she thinks it's one of those rare, bizarre situations unfortunately that befell her family. A fascinating woman and a very brave women I have to tell you. And a woman in therapy I hope. Yes, yes, a lot of therapy but also in a place of sort of forgiveness and trying to move on with her life and this is, for her, a chance to finally let it all go. Wow. Well, whew. Thanks to Deborah Roberts. The "20/20" two-hour special "My father btk" airs tomorrow at 9:00 P.M. Right here on ABC. And get the book. It is fascinating.
This transcript has been automatically generated and may not be 100% accurate.