It looks callous. The perfect nanny, here now, Elizabeth vargas and David Muir. A doctor and husband sits behind bars sitting there wa waiting. David, I have covered this story since it began five... See More
It looks callous. The perfect nanny, here now, Elizabeth vargas and David Muir. A doctor and husband sits behind bars sitting there wa waiting. David, I have covered this story since it began five years ago. One question kept coming back, how could a picture-perfect marriage crumble so quickly? Healthy wife found dead in the bathtub, did it have anything to do with the family's perfect nanny? Or was she? Reporter: Michele somers was a fresh-faced beauty queen from California. A sometime model with a string of suitors. But it was a handsome, aspiring doctor named martin Macneill who made her fall hard and fast. They eloped when Michele was 21 and, soon afterward, started a family. She had four kids in five years. So we just -- Mm-hmm. Boom, boom, boom. Reporter: Alexis and Rachel Macneill grew up idolizing their father. We thought, what an inspiration to become a doctor, to become a lawyer. I wanted to, you know, follow in my father's footsteps. I always wanted to be a doctor just like him. Reporter: A doctor who didn't just help heal his patients but who also taught Sunday school at their local Mormon church. And who seemed to have a heart big enough to adopt three young Ukrainian orphans -- elle, Giselle and Sabrina. So from the outside looking in, it sounds like the perfect family. Yeah. Reporter: If you're thinking it seems too good to be true, you're right. Take a closer look at the picture-perfect patriarch, and a different image begins to emerge. Not the typical father. He was just very -- Very haughty. Stern, haughty. Arrogant. He thought anyone that was not at his educational stature, was very beneath him. He treated them very poorly. Reporter: When the family moved to the Utah community of pleasant grove, next-door neighbors Doug and Kristi Daniels couldn't help but notice the contrast between martin and Michele. She was very quiet, was always very pretty and very well-kept. All the girls were just dressed perfect, like a tea party. Reporter: But the Daniels say martin was a braggart and a boor. If martin was ever around, it was him that always dominated every conversation. You could tell that he had a huge ego. He just made sure to say that he was downsizing into his home, and that he was a doctor and a lawyer. Reporter: His daughters found themselves apologizing for their dad. I was constantly trying to explain my father. When he would come home, he was a completely different person. So, we thought we knew the real person. Reporter: It was martin turned 50, the quirks they always defended became stranger. He became obsessed with the way he looked. He started tanning a lot. Reporter: You mean like a tanning salon? He'd go to the tanning salons. He lost weight. He'd start exercising just all the time, just in the middle of a conversation, jumping and doing push ups, things like that. It was really bizarre. Really strange. Very out of the ordinary. Reporter: How did your mom react to all of this behavior all of a sudden? This focus on physicality? She was suspicious. Reporter: And even more suspicious, says Alexis, was when their father began disappearing for long stretches. This seemed less like a midlife crisis and more like an affair. When, Alexis says, Michele confronted him about it, martin made what seemed like the ultimate effort to change the topic. Newly fit and supremely tan, martin told Michele she should do some improving of her O your dad decided that your mom should get a facelift. Out of the blue. And my mom had never talked about that before or anything. She'd never been into plastic surgery. Reporter: So, how much convincing did it take for your mom to agree to this? Quite a bit, actually. She saw my dad tanning, getting all in shape, and so I think, you know, my mom was just a little concerned too. Oh, maybe I should do a couple things. You know, maybe that will help. Reporter: Wavering, but wanting to keep her husband happy, Alexis says Michele reluctantly agreed to the facelift. And my mom said, "You know, martin, let's just wait until this summer. I would be home from medical school for my summer break and so I could be there and help with the recovery. And my dad said, "Oh no, Alexis, you have spring break coming up in a week. Let's do it then." Reporter: In a week? My dad said we have everything set up. You know, the anesthesiologist is reserved. You need to do it. Reporter: April 3rd, 2007, just two weeks after Alexis says her father first suggested it, Michele undergoes a full facelift. Alexis says that martin insists the surgeon prescribe a powerful combination of painkillers and sedatives, almost never taken to recover from this kind of procedure. And the surgeon agreed? He knew my dad was a physician, so he thought, he knew how to dose different medications. It was just bizarre because, yeah, my mom was very sensitive to medication anyway. Reporter: Alexis, away at medical school in Nevada, came home to care for her mother. But the evening after the surgery she says her father abruptly told her to leave. He said, I need you to get some rest, Alexis. And I said, "No, I want to stay right here by my mom." He said, "I'll take care of her medicines tonight." Reporter: You say the next morning, when you saw your mom, she was heavily medicated. She was completely sedated and out of it. The next day, I mean, it took, pretty much a 24-hour period until she kind of regained consciousness and was able to talk to me. And she said, "Alexis, you know, your dad, he just kept giving me medicines." And I went right to my dad, and he goes, "Oh well, maybe I gave her too much. And your mother threw up, so then I gave her more medicine." I said, "Dad, don't give her any more medicine. I'm going to take over." Reporter: Alexis spends the next four nights taking care of her mother and monitoring her medication. Michele seems to be feeling better. But one morning, as Alexis was washing her mother's hair, she says Michele dropped a bombshell. She started to cry. She said, "If anything happens to me, make sure it wasn't your dad." And I said, "Mom!" "What do you mean?" And she just said, "You know make sure if anything happens to me, it wasn't your dad." Reporter: Alexis alone knows her mother's terrible secret fear. But, Alexis would soon discover her father was keeping some secrets, too. Phone records revealed he was making calls at all hours of the day and night to the same number. Who was on the other end of the line? See what's next.
This transcript has been automatically generated and may not be 100% accurate.