Feb. 25, 2011  -- In April, 2007, two weeks after 50-year old Michele MacNeill died following a routine facelift, her husband Martin moved his girlfriend, Gypsy Willis, into the family home. Willis, he said, would be his young children's nanny. CLICK HERE to read part 1 of this story.

MacNeill's grown daughters, Alexis and Rachel, now estranged from their father, were worried about their younger sisters and were searching for answers about their mother's death. They created a file on their father, a long-time local doctor who also has a law degree from Brigham Young University's law school.

CLICK HERE to see photos of the MacNeill family.

Together with their aunt, Linda Cluff, Michele's sister, they started asking questions. Cluff visited a detective at the Pleasant Grove, Utah, police department

"He said, 'We're closing the case,'" Cluff said she was told. "'Sorry, you know, I know that kind of shocks you because she was young to have a heart attack.'"

Pleasant Grove police declined to discuss the case with ABC News.

But the women would not give up. For more than a year, they documented MacNeill's past and tried to get someone to listen to them.

"I'd try to go to the authorities. I'd go to the governor's office," said Alexis. "I went to every single newspaper in Utah, trying to get someone to listen. … I cannot understand why no one would listen. My mother was murdered … and no one cares."

No one, until they found veteran Utah County Attorney's office investigator Doug Witney. When Witney reviewed the women's file and official reports, he began to ask questions about MacNeill -- questions that led him all the way back to MacNeill's college transcript, three decades earlier.

"It appears to me that instead of taking his transcript and altering it, he got somebody else's. It had different entrance dates," Witney said.

Witney discovered that the 23-year-old MacNeill used that phony transcript to get into medical school in Mexico. MacNeill had told people he stayed a year. But when Doug Whitney tracked down that transcript, it revealed, "he [MacNeill] had actually been there for a semester," Witney said. "It was very obvious … [it] was totally falsified as well."

MacNeill's entire career in medicine was "based on … falsified transcripts to get into two colleges," Witney said. "How can he possibly be a doctor when he didn't have the transcript to even get into medical school?"

How did MacNeill do it?

"The guy is brilliant." Witney said. "I am not saying that he is not smart … he just … lies."

Witney said MacNeill next used the phony transcripts to get into a medical college in California, where he graduated after three years with a degree in osteopathic medicine. In 1984, he landed a residency at a New York City hospital, and from there built a 30-year career as a doctor. Among other positions, he worked at the Brigham Young University health clinic for nearly 10 years, but resigned following a complaint.

But that wasn't all. Witney discovered MacNeill served in the U.S. Army for less than two years in the mid-1970's, and was discharged for a psychiatric disorder. Witney discovered that over the next three decades, MacNeill was able to collect more than $100,000 in disability payments from the Veteran's Administration. By the time Utah investigators uncovered it, the amount was up to up to $3,000 a month. The VA confirmed to ABC News that MacNeill collected benefits, but the agency would not comment further.

And there was more. As Doug Witney peeled back the layers, he discovered MacNeill was put on felony probation for three years in 1977 for writing phony checks in California. According to Gary Ryan, a former assistant district attorney in Orange County, MacNeill had used the checks to pay for, among other things, home furnishings, jewelry, 60 pairs of socks, two dozen pairs of shoes and a year's supply of chocolate-covered cherries.

A 'Talented' Felon

A store employee suspected MacNeill was using phony checks and alerted police.

"I remember him because he was bright and he was a con, and cons always interested me," said Ryan, who prosecuted MacNeill. "They were people who if they had pursued legitimate things in their lives should have been a success. And he should have been a success. He had all the talent in the world."

It was a talent he turned into a career posing as a doctor for three decades, said Witney.

"Here is a man who went to jail for 180 days; was put on felony probation -- or parole -- for three years; was on felony parole when he went into medical school," he said.

MacNeill's daughters, Rachel and Alexis, were shocked to discover the father they adored had a criminal background and fraudulent credentials.

"The father we knew … he was just a façade," said Alexis.

"He was able to hide an entire life from us," said Rachel. "We basically found out that our entire lives had been based and surrounded on lies. That everything about our experience with our father was a lie."

Next, investigator Doug Witney and Jeff Robinson, Chief of the Bureau of Investigations for the Utah County Attorney's office, took a closer look at MacNeill and his relationship with the woman now living in the house as the "nanny," Gypsy Willis.

Witney said MacNeill and Willis apparently met in a chat room on the Internet. Investigators believe MacNeill communicated with many women over the years, but that his relationship with Willis started to take on a life of its own.

"I truly believe that she believed that she could control men by an aura about her," said Witney. "He eventually put her into an apartment that he paid for … and then their relationship became very heated."

After Michele MacNeill's death, Willis eventually took MacNeill to Wyoming to meet her parents -- Harold and Vicky Willis.

"He said, 'I never loved Michelle, but I love Gypsy,'" said Vicky Willis. "And I said, 'but you had a family with Michelle'… He says, 'Actually, I loved her as a friend, I loved her as a sister, but I never loved her like I love Gypsy.'"

Martin even proposed to Willis in front of her family, at a restaurant in Wyoming. Willis' sister, Julie, was there.

"He gives this grand speech about how he loved her, and how he loved her from the moment he saw her," said Julie Willis. "And he knelt and proposed to her, and Gypsy cried. It was very fairy tale."

But the fairy tale apparently had a dark side. Gypsy Willis was no princess, according to her family, who feuded with their daughter for years.

"I would consider Gypsy to be a deceptive, malevolent, malicious, calculating, person," said Julie Willis. "If she sees something she wants, she will rationalize that to the point that she will get that no matter who stands in her way."

And what she apparently wanted, according to investigators, was Martin MacNeill, who was married, with eight children. Witney said he interviewed Willis' roommates.

"She would have just a tirade, 'I have got to get rid of this woman that's between me and this guy," said Witney. "According to the roommate, she talked about 'cutting the brake lines.'… If the statements we are getting are correct -- we are talking about a woman who would have done just about anything to have her man."

But as investigators dug deeper, they discovered what appeared to be MacNeill's latest deception. It involved making one of his adopted Ukrainian daughters, Giselle, disappear.

Father Steals Adopted Daughter's Identity

A couple of months after her mother's death, Alexis MacNeill got a request from her father. He wanted her to take Giselle back to Ukraine, for a long-planned visit with her biological sister. Then 16-year-old Giselle packed a small bag and her Ukrainian passport. MacNeill kept her U.S. passport. Alexis flew over with Giselle and left her with her sister.

"My dad had just basically said … 'We'll get her after the summer,'" said Alexis. With Giselle gone, MacNeill took Willis to apply for a new Social Security card – using Giselle's name, Witney said.

"They went into court and changed the birth date 20 years," said Witney. "That's called perjury. … Now there are two people with that Social Security number, two people with that name."

Then, they went to court to change Giselle's birth certificate. MacNeill claimed Willis was his daughter, Jillian MacNeill.

According to Alexis, her father "was able to change the birth certificates around, and transfer my mother's house that was still in my mom's name." Investigators believe MacNeill was attempting to put the family home into Willis' hands.

Meanwhile, it had been nearly a year since Giselle left and she was languishing in Ukraine. Her older sisters were worried. Without telling MacNeill, their cousin Jill Harper traveled to the Ukraine to check on Giselle. She said conditions there were terrible.

"I walked in the bathroom and the walls were covered in mold and rust," said Harper. "There was a little pan on the floor in the bathroom, and I was like 'What's that in the bathroom?' And she's like, 'That's our shower. You just stand in there' … I mean I don't even know what movie I've ever seen anything that horrible in."

Jill Harper decided to take Giselle on the long journey back to Utah. In the meantime, Witney discovered MacNeill and Willis had applied for multiple fake ID cards.

"You are talking about a state ID Card. You are talking about bank accounts that were opened up under false names, false Social Security numbers," said Witney. "... We don't know why these people did what they did …because it was so likely that they would be caught," said Witney.

And they were. On Jan. 15, 2009, on what would have been Michele MacNeill's 52nd birthday, Witney and Robinson, along with federal authorities, moved in. MacNeill was arrested after landing at the Salt Lake City airport.

"And he was just headed right off the plane. It was quite a surprise," said Jeff Robinson. "He had no idea what was going on … and that was the beauty of it."

Willis was arrested the same day at the MacNeill home. According to Witney, MacNeill and Willis may have been planning to sell the house and leave town. MacNeill pled guilty to two counts of aggravated identity theft. Willis pled guilty to a related fraud charge. They were sent to federal prisons in Texas. Willis received a two-year sentence; MacNeill received a mandatory four-year sentence.

Alexis MacNeill saw her father at his final sentencing hearing.

"The only thing he said to me is …'I hope you're happy with what you've done,'" she said.

In a statement to the court, MacNeill reportedly denied he had anything to do with his wife's death. But with MacNeill and Willis now in prison, Witney collected evidence that might link them to Michele MacNeill's death. But it would not be easy, because this was now a circumstantial case. Pleasant Grove police did not treat the house as a crime scene, collect evidence, or interview anyone but Martin MacNeill. The medical examiner ruled the manner of Michele MacNeill's death was "natural."

So, Witney interviewed witnesses police never did. And he attempted to piece together a detailed timeline of what happened that morning. Witney focused on apparent discrepancies between what MacNeill told people and other witnesses at the scene.

Homicide Investigation: 'We Believe We Are on the Right Track'

The investigators also wanted to confirm what prescription drugs were in Michele MacNeill's system the day she died. They asked a toxicologist to review the original toxicology report, which showed an unusual combination of powerful sedatives and painkillers, including Oxycodone, Valium, Lortab and Ambien. Investigators wondered if the results could convince the Utah medical examiner to rule that Michele died under suspicious circumstances. After all, Michele MacNeill had the surgery a week earlier and had told her daughter she was feeling better that morning.

ABC News has learend the Utah medical examiner's office recently revised Michele MacNeill's manner of death from "natural" to "undetermined," with suspicious circumstances.

Witney wouldn't discuss further details of the ongoing investigation, but did say this to ABC News: "The reason we have a homicide investigation is that we believe that there is probable cause … there is foul play involved here … and we believe we are on the right track."

This past fall, the investigators travelled to Texas to try to talk to MacNeill in federal prison. But he wouldn't see them. Nor would he or Gypsy Willis talk to ABC News, despite repeated requests. Investigators are trying to determine if Willis had any involvement in Michele MacNeill's death, but won't say more than that.

It's believed the two still write to each other from prison, which is where both of their families hope they will remain.

"She belongs in a controlled facility where she can't hurt anybody," said Gypsy Willis's sister, Julie. "I'm sorry to say, but she does hurt people, and she will continue to hurt people to get what she wants."

Alexis and Rachel MacNeill say they will do everything they can to help in the Utah County investigation of their mother's death. They say they worry about what will happen if their father is released from prison, as scheduled, in two years.

"I'm afraid for my little sisters' safety," said Rachel MacNeill. "And for anyone he comes into contact with for the rest of his life. He is a predator."

Last week Gypsy Willis appeared in a Utah state court, facing additional fraud charges. She is due to be released from federal prison in March.

Doug Witney was elected Utah County Commissioner and is no longer on the case. The case report he and Jeff Robinson are preparing is expected to be presented to the Utah County Attorney in the coming months. In light of the county's investigation, Pleasant Grove police said they have re-opened their case.

Rachel is living in and working in California. She has created a Web site to honor her mother and one to gather more information about her father. Alexis graduated medical school and moved back to Utah to take a medical residency. She has custody of 9-year-old Ada and two of the girls her parents adopted from Ukraine, Elle and Sabrina.

Alexis, who recently married a fellow doctor, has taken her mother's maiden name -- Somers. She said she is proud to be a doctor, but will never be called Dr. MacNeill.

CLICK HERE to watch the full story on on the latest episode of '20/20.'

CLICK HERE to read coverage of the MacNeills' story in the Deseret News of Utah.