A recently married bride dies a mysterious death. Leaving her family at a loss for years. Well tonight new developments are pointing to her handsome doctor husband who has been married five other... See More
A recently married bride dies a mysterious death. Leaving her family at a loss for years. Well tonight new developments are pointing to her handsome doctor husband who has been married five other times and had another wife die unexpectedly. Here's ABC's Jim Avila for our series "Crime and punishment." Reporter: Down on the gulf of Mexico in the once sleepy lumber town alabama, a dark mystery of sudden unexplained death. This interview is with Michael Allen. Reporter: The husband who is not a suspect. The wife who died suddenly. Do you know the cause of death? Reporter: But was not murdered. Unless she was. What do you think really happened, Chester? I have to say this -- I think someone murdered my sister. ? Reporter: Shirley fell for the doctor, fell hard and fast, how do you do to I do in three months flat. Shirley wasn't his first bride, or second or third or even fourth. Shirley was number five. Some with tales to tell about their marriage to Mike and more importantly how their marriages ended. To be fair, this was wedding number five for Shirl Shirley too. In northern Alabama, Shirley's family the Thomases wanted to be happy for her. But they could not. I didn't like him at all. I just have to admit that. Reporter: Shirley was sold on her new man. Dr. Mike as he was called worked much of his life as a chiropractor. Adjusting grateful patients' backs in the nearby Florida panhandle. Smiling handsomely in health care ads in the newspaper and online. But money trouble plagued the chiropractor like a crooked spine and his financial problems troubled Shirley's family because Shirley had $1 million in the bank. Were you worried about her money? Yes, I was worried about her money. He came into her life with the clothes on her back. He come into the marriage with a wore out pick up truck and a bunch of debt. Her engagement ring from Dr. Mike, the wedding rings, the house they lived in, the family says, Shirley paid it all. Four years into the marriage something is wrong with Shirley. Months later, in a recorded interview obtained by "20/20," Dr. Michael would tell investigators Shirley had been ill for weeks. She gets bad migrais, two, three times a year. Reporter: The family says Mike tells them Shirley might have fallen down these stairs a few days earlier. While he was away. Knocking down a potted plant. He later tells investigators too. I sat here with her mother and asked her, baby, do you remember falling down those steps because that plant was knocked over? She almost got irritatedly mad at me. She said I did not fall. Myrtle and Mike nursed Shirley through the weekend the they tried to get her to go to the doctor. But Shirley keeps putting it off. Mike gives her migraine medicine. Seems to do a world of good. By Sunday night. Shirley is sitting up, eating, talking. Shirley, you better lay down and go to sleep. That's the last words I said to her. The next morning, Mike goes into the bedroom once again. She wasn't responsive. So I walked over and I turned on the light. And her lips were already blue. Mike yells for myrtle. She is not breathing. Call 911. Steve Brandon is a former FBI agent now a private investigator hired by the Thomas family. He showed us around the house on camelot. So when myrtle gets in here, what does she see? She sees Shirley on the floor. Myrtle knows it is too late. I said, Mike, Shirley is gone. The family is heartbroken and a little baffled. Bewilderment turns to suspicion when Shirley's daughter Sharon finds an old newspaper article. It is a brief story about the sudden death of a young woman in Gainesville, Florida, in 1977. Lynn, Mike's first wife. The article says a 25-year-old woman apparently choked to death Friday on a threat lozenge. Sharon and the rest of the Thomas family say they find two things strange about that. First, an otherwise healthy 25-year-old woman chokes to death on a cough drop. Second, they say Michael had always told them, a different story. He told them his first wife didn't die suddenly, she died a slow, painful death, from cancer. Michael told us the entire time he was married to mama that Lynn had leukemia. It made me wonder, what else has he lied about? What else has he lied about? For the answer to that question we take you to Florida and the suspicious fire in Dr. Mike's past. Nearly 20 years ago. In the place of business, detected smoke. Seen smoke. The lieutenant in plain clothes was a rookie patrolman back in the day. He says he found Dr. Mike standing outside his own office, just watching it burn. My first question was why didn't the doctor call the fire department? But that wasn't the cop's only question. Once I approached him, I detected the smell of diesel fuel on the person. That was before they found the can of diesel fuel and a match and the suspected motive. He was flat broke, and after the insurance. The doctor was arrested. Tried and convicted of arson. Shirley's family is devastated. I intend to see that he is dealt with and he can take that to the bank. A flicker of suspicion about what happened in the house on camelot court is now a raging five-alarm mission for what they see as justice. That is fully engulfed, three generations of the Thomas family. And lead to two more of Dr. Mike's five wives. So I just get on the internet and start face booking. Wife number two, Paula says he never harmed her, but relentless Sharon has tracked down yet another wife, number three T. Gloria Potts. Hi. ABC news was there when Gloria met Shirley's family face to face for the first time. She believes that toward the end of their marriage, Michael was trying to poison her. I felt lake I was being poisoned. I, I really did. You got sick? Sick. Couldn't hardly move. Then that's when I turned around and told her, Gloria, I can't believe you are saying this to me. I said mother has the had the same symptoms. The family of wife number five, Shirley, wondered if Dr. Mike had been trying to poison her too. And you guessed it, here comes wife number four, Diana. Today's date is February 4, 2011. En a rico in a recording, investigators questioned the fourth stop on Dr. Mike's matrimony trail. The wife between Gloria and Shirley. I think the man is dangerous. Near the end of her in the view, Mike's ex-wife makes a chilling request. I will be honest with you. If something happens to you. He need to be investigated. Now two more wives suspect Dr. Mike was frying trying to poison them. One of them says, hold on, that's not all. Wife number three, Gloria, reveals, a terrible trauma she says happened in her marriage nearly 30 years ago. She says Dr. Mike, the man who had always killed her with kindness, tried to kill her with a mallet. And I was asleep. And, he hit me in the back of the head with the mallet. With a mallet. Yes. And -- all of a sudden the pillow went over my face. And his hand came under the pillow and covered my nose and my mouth. Gloria says she escaped by playing dead and then running out of the house. You want to the hospital. I went to the hospital. We told them I slipped in the tub. Did you ever ask him at any point why were you doing that? Why did you try to kill me? Yes. He told me he had gotten stung by a jelly fish, he worked in China. And that it was a reaction to the toxins. That's right. She says Dr. Mike's excuse for hitting her over the head with a mall mallet, the gel gjelly fish made him do it. Gloria told no one, not even the police. She had two children to think of. Aside from the one incident. Mike was never violent. Beside the fact he tried to hit you with a mallet he was a good husband. Other than trying to kill me he was a very good husband. Reporter: When Gloria told the family and police, this amazing tale of Mike's allege add take no one knew what killed Shirley. The autopsy was not finished yet. Imagine the reaction when months later the family is finally given the results. I was shaking my head. I scant beliecan't believe this. Cannot believe this. I can't believe this is happening. Why? Is blunt force head injuries. A hit to the back of Shirley's skull, hard. That is what killed her. When "Nightline" comes back -- So when you find out later on it is blunt force trauma to the head. Then there is no question in my mind that Michael murdered this woman. Murdered Shirley.
This transcript has been automatically generated and may not be 100% accurate.