It had been nearly a year since Donna Pulsifer left California, vanishing with her children during the summer of 1969. Then, suddenly, she returned. Her ex-husband Dick Pulsifer learned about it from mutual friends.

John Larson (Dateline NBC): Now during all this time she hadn't called you? She hadn't written you?

Dick Pulsifer: Never heard a word. Never.

Donna had been living in Illinois with Mike Kent, her boyfriend whom she would soon marry. And now, nearly a year after she first left California, she was unexpectedly back. But she had only one of Dick's children with her -- his son, Rich Jr.

Dick Pulsifer: Saw her, talked to her. Where's Michelle? She's with friends. I said, no, no, no. That don't work. I said, "Where she's at, I want to talk to her and I want to see her, and I want to know where she's at” – “That's none of your business.”

John Larson: “None of your business”?

Dick Pulsifer: It's none of my business, that's exactly what she said.

Donna, however, did allow Dick to take his young son for a ride. And during this ride, Rich Jr., who was still 6 years old, said some alarming things. He, too, had no idea where his little sister was -- hadn't seen her in months -- hadn't seen her since the day Mike Kent and Donna had packed them all up and left California. And little Michelle was not with them.

Dick Pulsifer: He said, "When we left, Michelle was not there." I said, "What do you mean, she wasn't there?" He said, "When we packed up, I don't know where she was. She just wasn't with us."

Angry and frustrated, Dick confronted Donna about Michelle’s whereabouts.

Dick Pulsifer: I figured, well, you know what, this is can happen to my son, I got him right now. I said, "I’m taking him." And say, "No you're not, I’ll call the police on you." And so we got into an actual yelling contest. I said, "This is over. This is done. I'm not doing this." That's when I went to the police department again to file a missing person this time.

According to Dick, the police referred Michelle’s disappearance to the Orange County District Attorney's office. But once again, he was asked who had legal custody of Michelle and was told that as long as Donna had custody and says she knows where the child is, there was nothing the police -- or Dick -- could do about it.

Dick Pulsifer: She's missing. And they would not do anything. I was so beside myself, I could have ripped the counter off because I knew there was something wrong. I didn't think anything violent or, you know, anything physical happened.

There was good reason for Dick Pulsifer to have such fears, because just days after his confrontation with his ex wife, Donna left California and disappeared once again -- this time taking Rich Jr. and the secret of where Michelle might be with her.

With no one to turn to, Dick kept searching for his children on his own, until sadly, the days turned into years. Dick went on with his life but not one day went by without him thinking about where his children might be.

And then in 1980, 11 years after Donna first left California, there was a break.

Dick Pulsifer was served with court papers -- a new request for child support. But Dick noticed something unsettling. Donna had requested child support for only one child, Rich Jr. -- not for Michelle.

She had divorced Mike Kent and was living in Wisconsin. Her address was listed on these documents. So Dick immediately got her number and called.

He talked to his son, Rich Jr., who was now 17 years old. Then he spoke to Donna, who unbelievably refused to tell him where Michelle was living.

John Larson: What is life like when you have to wonder and look at every little girl you see?

Dick Pulsifer: You're always seeing that child somewhere, walking through a crowd. Wow, that could have been her, you know.

John Larson: And this isn't like once a year.

Dick Pulsifer: No, it's all the time.

After Dick called Donna’s home, he and Rich Jr. reconnected as father and son. Within a year, Rich Jr. decided to move to California to live with his father.

As a kid, whenever he asked his mother about Michelle, she would change the subject.

Over the years Rich Jr. was haunted by something he remembered hearing late one night, back when he still lived with his mom.

Rich Pulsifer Jr.: I think it was my junior year. I don't recall exactly. But I woke up to her crying. Her bedroom door was closed. And I heard Michelle’s name and I also heard "dead." But I was not quite coherent, and I was just barely awake.

About a year after Rich Jr. moved to California, Dick took him to a hypnotist to see if he could remember a clue, maybe a distant memory that would lead them to Michelle. But the session proved useless.

Rich Jr. was forced to hold on to his fading memory of the last time he saw his sister alive.

He was 6 years old. It was the wee hours of the morning when 3-year-old Michelle woke him up.

Rich Pulsifer Jr.: She came, walked, strolling in the room and crawled up on my bed and asked me to hide her. You know, she said, "hide me."

John Larson: "Please."

Rich Pulsifer Jr.: Yeah. "Hide me."

John Larson: Did she seem terrified?

Rich Pulsifer Jr.: No. Just minutes, not probably -- not even a minute after that, you know, mom came in and took her out of the room.

John Larson: What did she say?

Rich Pulsifer Jr.: She didn't say anything. She just picked her up and walked her out of the room.

John Larson: Did you ever see her again?

Rich Pulsifer Jr.: No -- that was the last time.

Within a day or two, Rich says his mother and Mike suddenly decided to move away, saying they were leaving Michelle with relatives.

During their 11-year separation, Rich Jr. had no idea how badly Dick wanted to find his children. Now, after living under his dad's roof, his father's obsession to find Michelle also became his quest.

In 1987 or 1988 -- nearly 20 years after his little sister disappeared -- Rich Jr. called his mother demanding to know what really happened to Michelle.

Rich Pulsifer Jr.: And she just flat out said, "I’m not going to tell you." I said, "Well, you know, I’m her brother. Don't you think I have the right to-- to know?” And she goes, "Rich, you know, things happened. We didn't have a whole lot of money, and we couldn't keep all three of you. And be grateful that I chose you." And I asked her, "Well, is she still alive?" and she said, "yes." And I asked her, "Well, is she still under the last name of Pulsifer?" And she said yes. And I said, "Well, what's it going to take for you to tell me--" when she goes, "Rich, I’m not here to make a deal with you." And that was pretty much it. That was the conversation.

Had Michelle been sold or given up for adoption? Or maybe fallen ill and taken somewhere? And why would Donna be so secretive? Had Michelle been harmed? Dick had long since remarried, but he had never stopped looking for his Michelle. He scanned the internet searching names, even speaking once with a Michelle Kelly Pulsifer. But sadly, it wasn't his Michelle.

And then in 2001, 32 years after Michelle’s disappearance, Dick's relatives had a family reunion at a park in San Diego. It was there that a former sister-in-law was reminded about Michelle’s disappearance and about Dick's desperate attempts to find her. She offered financial help to hire a private investigator who might finally find Michelle.

Paul Chamberlain: When we were first hired to find Michelle Pulsifer, I assumed it would be quite easy and that this would take a matter of several weeks -- if not a month at the most.

Paul Chamberlain worked as an FBI agent for nearly 20 years. He handled hundreds of kidnapping and extortion cases before forming his own investigative and security consulting firm in Los Angeles, and taking on the search for the missing girl.

Paul Chamberlain: The facts as they were given to me sounded very much like a domestic problem. And that therefore, the child was probably out there somewhere, and not that difficult to find.

But after searching for documents, school records, and interviewing dozens of people, not only had Chamberlain not found Michelle, but he could find nothing to suggest Michelle Pulsifer even existed after she was about 3 years old.

Paul Chamberlain: I had the feeling that something terrible might have happened when we realized that standard investigative techniques were not finding Michelle Pulsifer.

The private investigator had never seen anything like it. As he'd later report to Dick, there was no paper trail, no one who'd seen her, no leads whatsoever. Nothing. When a father has searched so long, how much does nothing weigh? Almost enough to crush him.

Video   Help on the way for father? March 14: A photo of a little girl in a blue dress has the same haunting effect on a district attorney that is has on the girl’s father. Dateline NBC

Dick Pulsifer: When he said there's no record. There was no record of Michelle from 1969 on.

That's when Chamberlain took his files to the Orange County District Attorney's Office -- the same office where 34 years earlier, authorities told Dick that since he didn't have legal custody, there was nothing they could do about finding his missing little girl. But this time, they saw something in this case -- and in a small photograph from 1969.

Larry Yellin (Orange County Deputy District Attorney): She's just this little kid. I got the feeling very early on, in seeing this one little grainy picture, that is all we had at the time of this little blonde girl, and you kind of get an image of what she could have been maybe, growing up-- what her life could have been like, the things that she was deprived. And so, you are driven to find out what happened.

An investigator for the district attorney's office spoke to Donna, who was now married for a third time. She was living in Wisconsin. Her new name: Donna Prentice.

Finally, for the first time since leaving California, she tells her story.

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