The perfect nanny continues. Once again, Elizabeth vargas. Reporter: Michele Macneill is recovering from a facelift her daughters say she had only to please her husband, martin. Daughter Alexis gets... See More
The perfect nanny continues. Once again, Elizabeth vargas. Reporter: Michele Macneill is recovering from a facelift her daughters say she had only to please her husband, martin. Daughter Alexis gets ready to go back to medical school, still troubled by a strange warning she says her mother gave her about her father. But she is happy that Michele appears to be on the mend. The doctor said she was healing great. She looked great. Went out to sizzler, she had a, you know, a steak dinner. She was feeling great. They dropped me off at the airport. You know, I just remember looking back and seeing my mom and waving. Reporter: But the next morning, less than 24 hours later, there would be a 911 call from the Macneill home. My wife has fallen in the bathtub! Okay, is she conscious? She's not. I'm a physician. Reporter: Martin Macneill, a prominent local doctor, sounds frantic. She's unconscious! She's under water! Okay, did you get her out of the water? I can't! I couldn't lift her up! I let the water out! Reporter: Veteran 911 dispatcher Heidi Johnson was on the line. It was really hard to understand him because he was yelling very hysterically at me. Okay, is your she breathing? So I tried to calm him down and tried to get the information from him. Okay, do you know how to do cpr? I'm doing it! Reporter: In fact, martin hangs up not once, but three times in less than five minutes. And he fails to give an audible address. As a result, Heidi Johnson loses precious minutes figuring out where to send the ambulance. Meanwhile, martin sends the youngest Macneill child, 6-year-old Ada, next door to neighbor Kristi Daniels. She said, "um, my dad needs some help." Reporter: It was Ada, just home from school, who first found Michele unconscious in the bathtub. So, I ran in, and followed his voice into the bathroom and he says, "I've already called 911. I need a male's help." Reporter: A man's help to lift his dying wife from the tub? Crucial time passes as martin sends Kristi to call for her husband, Doug. And I just immediately went straight to her legs, and I grabbed her legs, and we lifted her out of the tub and onto the floor. Reporter: Doug says it is chaos in the bathroom, with martin veering from frantic attempts at cpr to fury. He would calmly be doing puffs of air, and then -- and then he would suddenly have an outburst of yelling you know, "Why? Why? All for a stupid surgery?" Reporter: In the midst of it all, the phone rings. It is Alexis calling from medical school in Nevada. She is surprised when her father answers. He said, "Your mom, she's in the tub. She's not breathing. I've called an ambulance." And then he hung up. Reporter: For Alexis, in that moment, her mother's terrible secret fears begin to crystallize. And I just dropped all my books and just started driving to the airport and I was just screaming. Just screaming. He killed her. That was my first instinct. He killed her. Reporter: Before you left, your mom said, "If anything happens to me, make sure it wasn't your dad who killed me." My dad had no idea that my mom had confided in me. And I knew I was the only one that knew this. So I needed to start figuring out what had happened and protect the rest of my family because my dad is a killer. Reporter: Alexis's older sister, Rachel, has also been trying to call home, and finally gets through to her father. I said, "Dad, what's going on? Is it something with mom?" He said, "Rachel, come home." And so I called Alexis and I said, "Alexis, I know that mom's dead, isn't she? She's dead." And Alexis said, "Yes, yes." Reporter: Stunned and grief-stricken, the two sisters return to their parents' home. Alexis takes Rachel aside. She walked with me into the closet and said, "Rachel, dad murdered mom. I know, I know he did." I said, "What are you talking about?" I thought Alexis might have just been -- Reporter: Overly emotional or -- Overly. Just devastated. Reporter: But soon, Rachel starts wondering. Her father's story of what happened doesn't seem to add up. Okay, do not hang up -- Reporter: Why would this experienced doctor hang up repeatedly on the 911 operator? And why would a seemingly fit man need another man's help to rescue his dying wife? It was very strange to me that he couldn't lift my mother out of the tub. Because he was finishing the downstair's basement a few days prior and I had helped him lift sheetrock in. Reporter: And Alexis had her own questions about Michele's pills. She asks her father where those powerful painkillers and sedatives are and how many did her mother had taken on a morning when she had been recovering well from her facelift. I said, "Where's the medicine?" And he said, "I don't know. I don't know where it is. Check in the garage." Reporter: But she finds no medications. When she asks her father again, he says they'd been thrown out. And why? It was making him too sad to look at, to see this medication. Reporter: The medicine? As soon as I heard that, things were just starting to add up. Everything was adding up. Reporter: Now, both sisters begin to suspect the inconceivable. Because Alexis tells her sister about something else that happened just weeks before Michele died. When her father had started to disappear for long stretches, Alexis says her mother asked her to do some late-night investigating. While he was sleeping, I went online and printed out all of his phone records. And we found this number that he'd been calling a lot. Reporter: A number being dialed day and night. Alexis did an online search. And it popped out the name of the person. Reporter: And it was? Gypsy Jillian Willis. And my mom was like, "Who's this?" I mean, we thought it was maybe some stripper or something. Who's named gypsy? Reporter: Who is gypsy? Well, meet gypsy Jillian Willis, a 30-year-old nursing student when she met martin Macneill in an internet chat room. Her screen name was "Phoenixsheeba." He told her his name was "Joe." He sent me a message. He asked me what I knew about quantum physics. Reporter: You bonded over quantum physics? There was jt instant chemistry. He was tall. He was handsome. He was very well-spoken. Reporter: Did you know he was married? I did. Reporter: And that didn't ring any alarm bells for you on the ethics front? Not at that point. I wasn't looking for a serious relationship. He told me that he had a perfect life, that he had a perfect wife. Reporter: A perfect wife and a suspicious death. Three days after Michele was found dead in the bathtub, her grieving family attends her funeral. And standing in the crowd that day? Martin's lover, gypsy. Why would you go to her funeral? Who invited you? No one invited me. I just found out where it was. Reporter: You crashed her funeral? I had felt sorry that I had been involved with martin inappropriately. I felt sorry. Reporter: And that was the way to show that sorrow was to go to her funeral? No one knew who I was. Reporter: Martin knew who you were. Martin knew who I was and that's why I was there. I knew it would be a hard time for him. Reporter: Gypsy isn't about to let martin's mourning distract him. She sends martin text messages in the middle of Michele's funeral. She had even sent him semi-nude photos, the day after Michele died. You did send him two suggestive pictures of your naked back. Why did you do that? I wanted to keep his attention. It's cold. It sounds heartless, I'm sorry. But I knew that he would be having a hard time, not thinking of me, and that was selfish. Reporter: You understand that from the outside looking in, you're having an affair with this man, the wife inexplicably dies, you show up to her funeral, send him text messages during the funeral, it looks like you've come in to claim your prize. I did not look at it like that. Reporter: But that's what it looked like to martin's daughters when they made another starling discovery. We'd come to find out that my dad had been dating gypsy for several years before my mom's death. Reporter:less than a month after his wife dies, martin Macneill moves gypsy into the house to care for his children. What do you think of gypsy? What questions would you ask? Tweet me, using hashtag abc"20/20."
This transcript has been automatically generated and may not be 100% accurate.