In September 2003, Donna told an investigator what happened to little Michelle.

The last time she saw her daughter was before she and Mike Kent packed up the family to leave their house back in Huntington Beach, California, in 1969.

She said since they did not have much room in their car and the long road trip to Chicago would be hard on a small girl, Mike had taken Michelle to stay temporarily with his mother who lived nearby. Donna agreed to this arrangement.

The next day, Donna, Rich Jr., Mike, and his son Jamie traveled to Illinois. Once they were settled, they would send for Michelle. That was the plan, Donna told the investigator.

But investigators later learned Donna never sent for Michelle. Years passed and no one reported seeing her again.

The more they looked into Donna’s story about Mike giving Michelle to his mother, Jane Lambert, to watch, the more Donna’s story appeared to unravel.

When Michelle was allegedly left with Mike's mother, relatives say Lambert was an alcoholic suffering from breast cancer and in no condition to care for a 3-year-old girl. Not exactly the type of person you'd think Donna would choose to watch her daughter, let alone raise her.

And there was something else: relatives say all those years Lambert supposedly had Michelle, no one ever saw her with a little girl.

Just three years after Donna and Mike left California, Lambert died. It was 1972. She was buried here at All Saints Cemetery in Des Plaines, Ill. -- less than an hour's drive from where Donna and Mike were living. Michelle would have been 6 years old at the time, yet Donna didn't attend the funeral. She never asked to see her daughter. She never even made a phone call.

So if Michelle wasn't with Jane Lambert, where was she? Had she been sold or adopted as Dick had feared? After more than 30 years of hope and heartbreak, Dick Pulsifer was no closer to knowing what had really happened to Michelle.

John Larson (Dateline NBC): At what point do you give up that hope?

Dick Pulsifer: When they tell me what happened. You know, why isn't she here?

Orange County investigators continued searching and soon new information surfaced about Mike Kent.

The boyfriend-turned-husband, and now ex-husband, had a criminal record -- with convictions for battery and violating restraining orders. He also had a history of alcohol and drug abuse.

By August 2004, the Orange County district attorney announced Mike Kent and Donna Prentice had been arrested for murder.

Video   'He was a good father' Jamie Kent proclaims his father's innocence in the death of Michelle Pulsifer. Dateline NBC

Mike was the first taken into custody. He reached out to his son Jamie Kent -- the little boy who also lived with Michelle but was too young to remember. He was only 2 years old when they left California in 1969.

Jamie Kent: He told me the day he was in custody in Lake County Jail, he called me and he just wanted to let me know, he says, “Jamie, I swear I never hurt that little girl.”

Larson: Who do you think did it?

Jamie Kent: My dad swore to me he didn't hurt that little girl. So I think Donna did it.

John Larson: Why would he not walk out the door that day and go directly to authorities?

Jamie Kent: He was in love. He was protecting Donna, I believe.

Mike Kent and Donna Prentice both pleaded not guilty.

As it turned out, Mike would never have his day in court. He was in poor health when he was arrested and died just six months later.

With Kent dead, Donna Prentice was about to stand trial for murdering her daughter, despite the case's obvious challenges.

John Larson: You don't have anybody.

Larry Yellin: Right.

John Larson: You don't have a murder weapon.

Video   Hoping to find missing girl alive March 14: When police interview a missing girl’s mother, it raises hopes that investigators could find little Michelle still alive. Dateline NBC

Larry Yellin: Right.

John Larson: Do you have a motive?

Larry Yellin: I couldn't comment on that.

What he could say is his team of investigators had exhausted all leads, talked to friends, relatives and former roommates in an effort to find Michelle -- or at least to find out what had happened to her.

Larry Yellin: We started this investigation thinking she was dead, but wouldn't it be great if we were wrong. And wouldn't it be great if we could reunite this now-adult girl with her long lost father.

John Larson: Maybe she did go to another family or ran away or grew up with somebody. How do you prove that's not the case?

Larry Yellin: Because of all the avenues that we went to, all the hints or clues we could have had, all lead us to the sad conclusion. And that is: she was dead and she never left that house in Huntington Beach alive.

So what really happened to Michelle? Was her death an accident? Had an angry parent hit her too hard? Or was she deliberately killed?

Whatever the answer would turn out to be, the prosecutor said it was time someone besides her father stood up for little Michelle, so he would -- in court.

John Larson: What is it about that 30-year-old grainy picture of that little girl?

Larry Yellin: Because she's anybody, which means she's everybody, you know. And we should not let her just be lost and forgotten.

Now jurors were going to hear not only from Donna herself, but also from Mike Kent -- in his own voice, from beyond the grave. Would the mystery of what had happened to the girl in the little blue dress finally be solved?

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