Did Utah Doctor Kill Wife to Be With Another Woman?

Prosecutors allege Dr. Martin MacNeill is a manipulative adulterer who wanted his wife gone.
8:20 | 10/18/13

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Transcript for Did Utah Doctor Kill Wife to Be With Another Woman?
Today in Provo Utah opening arguments in the case that -- two daughters. Against their own father the question did a prominent doctor murder his beautiful wife and the couple's bathtub. And did he do it to make Rome for his mistress. They seem like the perfect couple and in the case full of twists and turns his -- believe. He almost got away with murder here's my co anchor Dan Abrams for our citizens crime and punishment. That. Why can't help you. They have good Martin McNeal sat stone fittest is his frantic 911 call was -- troops and the Utah courtroom at least by parents -- It can't I breathe and can not only hope we can I don't -- And part -- it. -- is charged with killing his wife Michelle. A former beauty queen and mother of eight in the bathroom of their suburban home your whole thing but -- -- -- that you never want to come to trial to. If not for the single minded determination. Of Martin's own daughters. Who say they're trying to hold him accountable. For the death of their beloved mother in 2007. My father. Planned and orchestrated. My mother's my mother's death. He was yes he did and and he thought he'd get it could get away with that. He explained to a final witness. He was glad to -- was dead. Prosecutor painted a portrait of McNeil as a man who used his own medical training -- particular sleep planned the murder of his wife. And even bragged about it after -- the defendant told this witness. That it would be hard to prove it was murder. Because authorities could conclude his wife took too many medications. And accidentally fell asleep in the -- but the defense argues the evidence against in his purely circumstantial. Is wrong things. Our -- video is not -- they acknowledge that McNeil now 57 had affairs and is no Angel. But insist he's no killer -- there we probably should. Let emotions cloud our judgment. We may make. -- And that's natural. It is very critical that during this trial is set aside your motion. And you evaluate this case based upon the facts. This strange saga began on an April morning in this gated community south of Salt Lake City. To start sending Martin McNeal cold -- when -- -- Born in the top -- -- -- -- -- -- hung up on the dispatcher was disconnected twice and provided the wrong address. This man lost precious minutes in the fight -- Michelle's life. And maybe most troubling. He said he couldn't remove his dying wife in the bathtub alone. When police showed up -- said his wife passed out while preparing the top and they soon ruled it an accident. After all they had no reason to suspect -- a family man a prominent local doctor and leader in this conservative Mormon community. The medical examiner determined the official cause of death to be from natural causes. Said the case seemed to be closed. I thought that if this is a healthy. Woman that died that there would be some sort of big police investigation. Their police report -- my mother's death is about. Two and a half aircrafts. But daughter Alexis was suspicious to say the least. She says just days before her death. Michelle McNeal shared a startling secret. She said if anything happens to me make sure wasn't your dad and I -- -- -- What do you mean you know what -- -- she's just sent. You know make sure if anything happens to me if there wasn't -- This was the same father Alexis and Rachel had grown up idolizing we thought what an inspiration. To become a doctor -- become a -- I -- and setting -- on my father's footsteps I always wanted to be a doctor just I can. But after his fiftieth birthday they -- things changed at their dad became obsessed with his appearance working out feverishly and visiting tanning -- There were also unexplained disappearances from home. And finally they say he suddenly insisted his wife the former beauty queen get a -- slipped. And the -- never talked about not before anything had never. Been into plastic surgery so why would this doctor want cosmetic surgery for a woman he was hoping to remove from his life. According to prosecutors. So we could administer or over administer a powerful cocktail of painkillers and sedatives as she -- Alexis asks the defendant what he had given her. He stated that he would probably over medicated her Lexus began to track all of the food. Beverage is medications. And other things consumed by Michelle. In addition to taking her vitals. As she recorded -- hold this information and a little -- she kept near Michelle's dad. The motive according to prosecutors. This woman Gypsy Willis with whom McNeal was allegedly having an affair but this was no Flint. Shortly after Michelle's death he moved Gypsy into his home and announced that she would now be the family's new nanny. She didn't cook she didn't clean. Shouldn't take care of the children anyway. Michelle's daughters wrote letters to newspapers and pleaded with the authorities but no one would listen. No one that is and to talk to this. Investigations -- -- winning veteran investigator Doug Whitney at the Utah county attorney's office -- -- neighborhood are elected office and started to investigate. I would simply say that I believe that. Mark -- as a sociopath. As Whitney chipped away he learned troubling -- -- so that mark -- -- -- -- His entire career is based on falsified transcripts from different colleges we basically found out that our entire lives had been based in surrounded on lives. Everything about our experience with her father was -- -- Investigators say -- in Gypsy. Teamed up to steal the identity of Martin's own adopted Ukrainian daughter and give it to Gypsy. Apparently so she could collect benefit. They went to court and change the birthday twenty years has -- perjury. Now there's two people without Social Security risk to people. The investigation finally led to -- conviction in 2009. On two counts of aggravated identity theft and Gypsy on a related fraud charge. The last sentencing hearing. Only thing he said to me as I hope you're happy -- I hope you're happy with what you've done. -- Martin and Gypsy locked away investigators turned their attention to Michelle's death. And pieced together the evidence to bring the murder case his daughters Alexis and Rachel had long sought. At a hearing last year. The women even held up photos of their mother in the courtroom. You've got all of this evidence that sure seems to implicate Martin -- you've got his own daughters who think that he ought to be convicted. And -- you're saying this is not a slam dunk for prosecutors. It's not a slam dunk for prosecutors despite all the evidence they have there's a critical piece of evidence that the -- -- not here and for good reason. And that is -- -- shall -- statement to her daughter. A few days before she died if anything happens to me make sure your -- -- talent. And today the defense argued there's no evidence that -- show was even murdered at all while the investigation. Subsequent to Michelle's death. Raises questions about the possible role -- her husband. There is nothing any autopsy. And toxicology findings that proves her death. Was from an unnatural costs as for -- -- daughters they see their hopeful. That this could be the end of a long journey for justice. This was very well planned -- he almost got away with it and let's hope that the jury. Convict my father.

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

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