Reporter: It's a southern-fried mystery. A one-time millionaire shirley seitz dies suddenly in what we will soon see may not have been sweet home alabama. Her family suspects foul play everywhere they... See More
Reporter: It's a southern-fried mystery. A one-time millionaire shirley seitz dies suddenly in what we will soon see may not have been sweet home alabama. Her family suspects foul play everywhere they look. And dr. Michael wohlschlaeger -- they're looking at you. He just didn't act right. To me, he just didn't act right. Reporter: You started to have questions about what happened to your mother? Absolutely. I did. Absolutely. Reporter: The suspicions begin with dr. Mike's reaction to their surprise visit back when shirley was sick. Dr. Mike items investigators, in that interview obtained by "20/20," he was happy to see his inlaws. I said, "boy, this is just a real godsend." I said, "shirley's been sick for the last three days, with one of her migraine headaches." And, I said, "here you are, showing up." Reporter: Shirley's mother, myrtle, and brother, junior, say that's not how they remember it. He acted very shocked that we were there, and asked me, "what are you all doing here?" Reporter: The family also wonders about that knocked-over flower pot. When we went in, we noticed a flower pot that was laying in the floor and I asked him about that. Reporter: Mike said it showed shirley might have fallen down the stairs a few days earlier while he was out of town at a doctor's appointment. He tried to tell us that -- that she had fallen, I guess down the stairs and knocked this flower pot over, you know. And that's how her -- what -- what was causing her head to hurt, you know? Reporter: But the family suspects that is a little too convenient. They speculate mike was staging things to back up a phony story that shirley had fallen. Thomas family investigator steve brannan. When the mother comes in on friday, this flower pot that was supposedly knocked over on wednesday is still knocked over. It's not been setup or cleaned up. Reporter: It's still there. Yes. Two days later. If I turn a flower pot over in my house, I pick it up. I don't let it lay there for two days. Reporter: Something else bothers myrtle. Michael's activities on the morning shirley died. On the way to the hospital, myrtle says she told him she noticed a spot, maybe blood, maybe something else, on the bed where shirley had slept. I said, "well, I want to know what that red was on the sheet." He said, "there wasn't nothing red on that sheet." Reporter: Whatever it was, the family says, mike was very quick to clean it up. When you got back to the house, did you go looking for the sheets to see what was on it? They was done gone. He'd done jerked them off the bed and had them in the washing machine to wash. Reporter: Dr. Mike later told police shirley got sick on the bed. Hasty laundering, a knocked over plant. Somebody not acting right. All suspicious, perhaps, but is this grieving family overreaching to blame someone? We don't like something that's ambiguous, none of us really like that. We want to know why something happened. Reporter: Psychologist jennifer hartstein says in cases like these, it may be the grief talking. And very often, while we're grieving, if we're angry, we might want some sort of retaliation, we think that they must have done it, so we're going to retaliate and go after that person. Reporter: But buckle up, because the thomas family is not going to quit. In fact, their hunt for shirley's will leads to a scene straight out of a tv cop show. While dr. Mike is out at a religious meet egg, the family conducts a frantic, clandestine search of the house. Mike could have come back through that door at any minute. So we was having to kinda sneak around and do what we had to do with one eye here and one eye there. Reporter: Sharon and her uncle take the place apart, drawer by drawer. We turned that house upside down. We were digging, digging, taking pictures, trying to find that original will to get in my hand. Reporter: They find the will, in which shirley, even after four years of marriage, left everything to her daughters. Not a dime to her husband. Why didn't she write him in? To the family, the answer becomes clear when they find something else. Shirley's journals. Personal, revealing journals. We found it in, actually, up underneath another drawer in her bedroom. Reporter: And is there anything of interest in the journals about their relationship? How much longer am I going to have to financially support this man? He said he wasn't going to do this to me, he was going to get a job. He's constantly spending my money. Lord, when is he going to get a job? Reporter: Later, when police ask mike about his marriage, he paints a totally different picture. How would you describe your and shirley's relationship? We had an absolutely marvelous relationship. Shirley and I were the epitome of just exactly what a husband and wife were supposed to be. Reporter: But when shirley's daughter reads some of the journal entries to "20/20," well, see what you think about this marvelous relationship. Nothing but take, take, take from this man. No giving. I'm not a wife. I'm a bank. That is taking care of all of his financial needs. Reporter: In fact, seven months after shirley's death, she was still helping to support him officially. Mike collected on her life insurance. 100,000. All the while, the thomas family is desperately searching for a smoking gun. Still ahead, they think they find one. At least, half of one. Not the gun, just the smoke. From a suspicious fire in dr. Mike's past, and a most curious discovery about the first mrs. Wohlschlaeger. Like shirley, she's dearly departed. And wait until you hear how she died.
This transcript has been automatically generated and may not be 100% accurate.