(ABC News) -- A man who spent almost four decades in prison for killing two people in the Arizona desert today pleaded no contest to two counts of second-degree murder and will go free.
Bill Macumber entered a plea in Maricopa County Superior Court under an agreement with prosecutors and received a sentence of time served. Although the victims' family asked Judge Bruce Cohen to deny his request, prosecutors said they couldn't pursue a third trial because key evidence had been destroyed or lost.
The 77-year-old Macumber, who had no history of violence, was convicted in the 1970s in one of the most sensational murder cases in the history of Arizona. Macumber was twice sentenced to life in prison for killing Joyce Sterrenberg and Tim McKillop, both 20 years old, and leaving their bodies in the desert. In total, he has served 37 years.
On May 24, 1962, the young couple was found shot and killed next to their car in an area now near Scottsdale. The case went cold for 12 years until Macumber's wife, Carol Kempfert, went into the Maricopa County Sheriff's Office department where she worked and told her supervisors that her husband had confessed to the murders. Macumber was arrested a week later.
In 1975, Kempfert testified against her now ex-husband, again saying that he confessed. During the trial, three pieces of evidence allegedly had been collected by investigators at the scene and were also presented: a .45 automatic pistol, a lifted palm print and bullet casings, according to the Maricopa County Attorney's office. At the time, prosecutors argued that the physical evidence linked Macumber to the murder scene.
Macumber was convicted of two counts of first-degree murder and was sentenced to two concurrent life terms that year. After successfully appealing his convictions, Macumber was retried in 1977 and again found guilty and sentenced to two life terms.
Macumber's son, Ron Kempfert, and the Arizona Justice Project have been advocating for Macumber's release for years, saying that Macumber's ex-wife framed him and that another man committed the murders.
Ron Kempfert, now 44, told "Nightline" in a 2010 interview that he had no doubt of his father's conviction, until he spoke with prominent Phoenix defense attorney Larry Hammond in 2003 -- 28 years after his father had been sent to jail. Hammond founded the Arizona Justice Project, an organization that works to free prisoners they decide could be innocent.
"He said, 'I don't know how to tell you this, there is no way to tell you this -- we know your father, we think your father is innocent, and we're pretty sure your mom framed him for it,'" Kempfert said of the phone call with Hammond.
After recovering from the initial shock, Kempfert said he started to untangle what his mother, Carol Kempfert, had told him over the years and slowly the possibility that his father was innocent began to make sense to him. He told "Nightline" he eventually came to believe that his mother had a powerful motive: Around the time she turned her husband into police, Carol Kempfert and Macumber's marriage was falling apart. At the time, she was working in the sheriff's office, where she had access to evidence from the cold case murder, and she had recently taken classes in lifting fingerprints.
Carol Kempfert also sat down for an interview with "Nightline" in 2010, where she denied 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 at the time. "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 crumbled.
"It sounds ... ridiculous. But that's, in fact, what happened," she said.
But adding fuel to Ron's 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."
In 2009, Macumber and his attorneys petitioned the Arizona Board of Executive Clemency, which in a rare move unanimously recommended his sentence be commuted, saying, "An injustice has been done in Mr. Macumber's case" and that his wife had "motive, means and opportunity to falsely pin the murders on Mr. Macumber."
Arizona Gov. Jan Brewer denied the recommendation for clemency.
In 2011, Macumber petitioned the Court for post-conviction relief and was granted an evidentiary hearing. But without the necessary evidence, prosecutors said in court today they were unable to retry the case for a third time. Now that the judge has accepted Macumber's plea, he will be released.
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