"It's just blatant lies," Macumber said in his defense. "That's all it ever was from the beginning."
Macumber, now 75, said he has done his best to fight off bitterness, but what he is most angry about is his ex-wife's efforts to destroy his relationships with his three sons.
"Quite frankly the most unforgivable lie she ever told was to her own children, even after I was in prisons he told them their father was a murderer, he didn't love them or care for them, and hadn't made an effort to contact them and that was a terrible lie. I wrote dozens of letters to my children and every one of them came back refused. They never knew I wrote, they never knew I cared, and as a result of that I've lost two of my boys. I hope she burns in hell for that," he said.
Now living in Olympia, Washington, Carol Kempfert agreed to sit down for an exclusive interview with "Nightline" -- her first and only television interview. To this day, she denies she fabricated her husband's confession.
"Absolutely not...I didn't wake up one more morning and say, "Oh, gee, I think I'll go frame my husband today,'" she said. "I did not, and I will say this again, I did not manufacture nor did I ever tamper with evidence. Ever. And I passed four polygraphs and I'll be happy to take another. But I did not tamper with any evidence."
Kempfert told of how Macumber came home with his clothes covered in blood the night of the murders, and that he later confessed to her as their marriage was falling apart.
"It sounds (pause) ridiculous. But that's, in fact, what happened," she said.
When asked how she felt about her son Ron turning his back and accusing her of framing his father, Kempfert blamed his actions on bad judgment.
"Critical thinking is not one of Ron's better skills," she said. "If anyone was ever made for Bill to mold and manipulate, it would be Ron."
Ron responded to his mother's accusations, "let's say I am gullible and my father is manipulating me but please tell me how he's manipulating the Arizona Justice Project?"
Adding fuel to his belief that his father is innocent, a man named Ernsesto Valenzuela allegedly confessed to three different people that he had committed the murders -- evidence the jury at Macumber's trial never was able to hear.
After Valenzuela died in prison in 1973, his former defense attorney, Tom O'Toole, came forward with his client's confession but the judge ruled it unreliable hearsay, reported The New York Times. O'Toole said attorney-client privilege kept him from presenting Valenzuela's confession until after his death.
"I believe [Valenzuela] told me about committing those murders because he got pleasure in committing those kinds of crimes and he relished it," O'Toole said. "He analogized shooting one of those people to it being like shooting a rabbit… he was thriving on it, he loved it."
Even after 35 years in prison, Macumber has been a model inmate. He's done charity work, counseled other inmates, was voted head of a local chapter of the civic group, the Jaycees, and even published a book of poetry.
He would have been eligible for parole 10 years ago if he'd agreed to confess his guilt, but he refused.
"Bill Macumber could never do that...he would rather die in prison than say he committed a crime he didn't commit," said his lawyer Larry Hammond.