Man in prison for murder of Tito Jackson's ex-wife denies killing her: Part 5

"I'll go to my grave saying that she could swim, because Delores could swim," Don Bohana told ABC News' "20/20."
7:21 | 09/16/17

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Transcript for Man in prison for murder of Tito Jackson's ex-wife denies killing her: Part 5
My father could not, did not, and would not ever, ever do what he's accused of. Reporter: November 1998, don bohana is on the way to prison, his daughter Donna begging for mercy. The judge presiding over the case rejecting her plea. Defendant is sentenced to the state prison for the term mandated by law of 15 years to life. Reporter: With that bohana marches directly to jail for processing and hasn't tasted freedom since. Today, locked away in a central California prison, where we interviewed him over the phone. So, don, let me ask you directly, did you kill Dee Dee? No, absolutely, absolutely no way. I wouldn't kill anyone. Reporter: One of the things that's tricky is we have all these people who said that she couldn't swim? I'll go to my grave saying that she could swim, because Delores could swim. Reporter: He's reserved his deepest anger over the defense. Right after I was guilty I told him I never want to see his face again because he just screwed me all the way. Reporter: Still enraged that Braun left his most important witness off the stand. Dr. Michael bauden. I was surprised. This is an incident man who has been in jail for a long period of time. Reporter:? 2002 bohana appeals his conviction on the grounds his attorney had bungled the case. I wish we could have won the case but it doesn't haunt me. Reporter: We take bohana's charges directly to Harland Braun, who counters that it's his own client who's to blame for the courtroom loss. He was not a good witness. To be honest about the case, the worst witness was Mr. Bohana. Reporter: But of course, it was Braun's decision to put bohana on the stand in the first place. Harlan never told me anything. I didn't have one bit of professional preparation. Reporter: Braun denies that. As to why the doctor was never called Braun says the veteran expert would have been a weak witness. I wasn't that impressed the way he was going to testify. You didn't think he would have helped? No. When you have Michael bawden ready to testify that the prosecution's theory doesn't hold up and you don't call it? Really hard to explain. Reporter: Bo Hanna suspects something more since ter affected the decision not to call Dr. Bauden money. At the time don is behind in his payment schedule and according to this affidavit an agitated angry Braun state ds it is not wise to have an attorney angry about nonpayment of his fee. He was implying that he was not going to do the best job because he was unhappy. Reporter: Did you make that statement? No, I never made that statement. Reporter: You weren't angry at him, and he wasn't angry at you? I didn't like the fact that he stiffed me. But I wasn't going to pull any punches on a murder case. Reporter: In fact, Braun says his trial strategy was to rely on his own cross-examination skills to destroy the prosecution's case by damaging their experts with his sharp questioning. It's always better to get what you want out of a prosecution witness than your own witness. Reporter: And in the end, the appeals judge rejects bohana's B claim, ruling that Braun's trial strategy was reasonable, leaving bohana to serve out the rest of his sentence. Another 14 years pass. The Jackson kids see their once-promising musical career wane, though they did have their own reality show last year. Never forgetting the mother who died so tragically, here driving to visit her grave on their show. To this day, I'm learning how to deal with it, but the pain is still there. Reporter: Meanwhile, Donna bohana has turned her grief into action. By day, she works as a glam realtor to the stars in malibu, California. But her nightly obsession, combing through every document in the case. Here she is in her bathrobe launching a legal treasure hunt to find some shred of evidence that might help get her father out of prison. These boxes have been in my family for 18 years. Reporter: And Donna hits what she thinks is pay dirt, digging up a bombshell about the d.a.'s tent pole witness, Dr. David posey. At the very time prosecutors are relying on Dr. Posey to indict don bohana another prosecutor, Steven Kay, from that same d.a.'s office, is going public with his claim that posey is a "Fraud," saying, "He just doesn't have the experience to know what he's talking about." Today, Kay, a highly regarded veteran prosecutor, stands by that claim, pointing out posey had only worked as a part-timer at the L.A. Coroner's office. He just dabbled in autopsies. Reporter: Dabbled? Dabbled. Yeah, he dabbled. I don't see any insurmountable problems in this case. Reporter: You may remember the sensational trial that Kay prosecuted in 1996. He was shocked by posey's testimony, this time for the defense in the case of an L.A. Raiders cheerleader who was strangled to death in back of a car. Using his then-wife as a stand-in, Dr. Posey simulated his claim that the cheerleader's death was actually an accident, something the jury soundly rejected. Kay says he would have been happy to have told fellow L.A. Prosecutor Lori Jones about what he calls posey's lack of qualifications if asked. I would have told her what I told you today, that his testimony should not be believed. Reporter: Nobody in your office raises the flag and says, "Wait a minute, we're using that guy ourselves in another courtroom"? I don't recall recall ever hearing until today you telling me about Dr. Posey, I don't recall ever hearing anything negative about him. Reporter: Does it concern you today? Sure it would ccern me, but it's not causing me to lose confidence in the outcome. Reporter: But that brings us to a question brought up at trial. Why did Dr. Posey change his opinion from undetermined to homicide? On the stand he testifies based on his visits to bow hoon that's pool and his own experience as a life guard he always suspected it was homicide and testifies the da's office told him they had an expert who confirmed his opinion but on the stand the doctor admits he never spoke to the expert nor read his report before he changed his conclusion. So we wanted to speak with Dr. Posey ourselves and made repeated requests to an interview all with no response. We would like to know why you changed your opinion on the case. I would have to go back and look at the case. You do remember the case of Dee Dee Jackson? The name is vaguely familiar. Been in prison for 20 years. I don't recall the testimony. If he doesn't remember testifying why am I sitting here? Cost me 20 years of my life I'll never get back.

This transcript has been automatically generated and may not be 100% accurate.

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