Scott Peterson becomes a prime suspect in his wife's disappearance: Part 1

Scott and Laci Peterson were college sweethearts. She was eight months pregnant with their first child when she disappeared. Authorities discover he was having an affair.
7:42 | 05/15/21

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Transcript for Scott Peterson becomes a prime suspect in his wife's disappearance: Part 1
Lacy went missing Christmas eve. She's 27 years old and she is 8 months pregnant. I knew he had killed her. Our family has known since the beginning that Scott is innocent. We have someone who goes missing in this window of time and you have a felony occurring in this window of time. To think that they're not related is a difficult thing to ignore. It's been 18 years and there should be answers to questions. I think if people step back and - look at the evidence in this case, they're going to see this crime isn't solved. I'm ready to go back to court. Let's do it again. I'd be ready to testify. He deserves to be where he is. Can I help you? Yes. My daughter has been missing since this morning. The story of lacy Peterson's disappearance made news soon after she disagreed. It was Christmas eve 2002. It became national news pretty She is carrying their first child. She's just weeks out from birth. Scott and lacy Peterson, I mean, it's right out of a romance novel. They were college sweethearts. Describe your son. He was a very affectionate, just a really kind, sweet little guy. Never in trouble of any kind. Lacy by all accounts was just a bundle of energy and was always concerned about helping over people. They had been married not very long. They had bought the house a couple of years earlier. Lacy was a homemaker. How did Scott feel about the fact that he was going to be a father? Very excited. Seems that when she got pregnant with Connor, things started going sideways. The first person you focus on in a homicide investigation is the person closest to the victim and the last person to see the victim. Boom, boom. We got both of those with Scott. He claims they woke up and he and lacy had breakfast together. He thought he would play golf, but because it was rainy and cold he decided not play golf but to go fishing. Scott finished fishing that day at some point in the afternoon and made a phone call to lacy. Hey beautiful. I won't be able to get that basket for papa. I was hoping you'd get this message and go on out there. I'll see you in a bit, sweetie, bye. He says when I get home, her car is in the driveway. I enter in the back gate. Mckenzie came running up to me. I knew that lacy was missing when Scott called that evening and asked if she was at our house. Immediately he came back saying she was missing. I remember feeling just a little agitated about that word, the word that he used "Missing." How can you be missing? She's not missing. There was no evidence of a struggle or tampering or forced entry. There was nothing missing from the house. So of course the police start looking at him. So he was questioned for over 7 hours the first night that lacy went missing. He just doesn't seem like the guy whose wife is missing. His demeanor was suspicious. We begin an immediate seshlg search of the park and river I always blame the husband and I am almost always right. I start with the presumption that the husband did it, but there were alternative theories. One was kidnapped by a satanic cult, another one was there was a burglary across the street. They needed to stay on Scott. They needed to do what they did. There's absolutely no physical evidence at all that Scott committed in crime. We pretty much dealt with all of the satanic cult the dog the only thing we couldn't eliminate was Scott. Earlier this week the Modesto police department was made aware of an article that was to appear in the "National enquirer" revealing new information regarding lacy's case. The family members were shown very recent pictures of Scott and a girlfriend. First of all, I met Scott Peterson November 20th, 2002. Scott told me he was not married. We did have a romantic relationship. Amber probably met with detectives and gave information about the relationship with Scott Peterson. Amber Frye has been eliminated as a suspect in the lacy Peterson disappearance. I was just starting my career in massage therapy. My daughter was very small. Single mother. He was good looking, he was nice, he was funny and attentive to me. She really thought she had Mr. Right. Scott new amber for 16 days when he got caught being married. He was very emotional and said that this would be the first holidays without her and he was crying at that point. I took it as she died, didn't know how, if an accident or cancer. I had no idea. I didn't pry. She didn't know about Scott and lacy missing until her friend told her. Hey, that guy you brought to the Christmas party, he's on TV every day. And so I went to the other room and called the Modesto police department hotline. Amber Frye started cooperating the police. I buy her a tape recorder with some cassette tapes and a wire that can look onto her phone. I told her, okay, if he ever calls, just push these two buttons and just talk normally. Phone rings and it's Scott Peterson. I'm like, that's him. Show time, girl. Amber. Hey, happy new year. Happy new year. I'm glad I caught you. Thank you. What they heard on December 31st, 2002, was a Scott Peterson, who while a candle light vigil is being held for his wife and he's attending it is also on the phone with amber Frye being recorded, unbeknownst to him, telling her that he's in Europe. I'm near the eiffel tower. It's unreal. This guy's wife is missing. The entire country is looking for her and he's not only keeping his girlfriend at bay, he's entertaining her with these outlandish lies. To commit a crime like this, you have to have a screw loose at the very least. Those amber Frye tapes made it seem like Scott Peterson has a screw loose. He now is enemy number one. Everybody hates Scott Peterson. Did you murder your wife?

This transcript has been automatically generated and may not be 100% accurate.

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