Dec. 20, 2013— -- A Wisconsin man could be one step closer to becoming a free man after he was sentenced to life in prison for killing his wife with antifreeze 15 years ago.
A federal judge in Wisconsin Wednesday overturned Mark Jensen's 2008 conviction, saying his constitutional rights had been violated because a letter that his wife, Julie Jensen, wrote before she died shouldn't have been part of the trial.
The letter has been described as a "voice from the grave." Julie Jensen, 40, wrote the letter and then gave it to her neighbors, telling them that if anything should happen to her, they should give it to police. Less than a week later, Jensen was dead.
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Jensen's neighbor, Margaret Wojt, read a portion of the letter to "20/20" in 2008.
"I pray I'm wrong and nothing happens. But I'm suspicious of Mark's suspicious behavior and fear for my early demise," Wojt read from the letter.
But in Chief U.S. District Judge William Griesbach's 33-page order, he wrote that the letter had a "substantial and injurious effect" on the verdict and that "a reasonable jury could perhaps reach the same verdict in a trial free of constitutional error."
From the beginning, Mark Jensen's attorneys argued the letter should not be admissible, that Jensen's depressed wife took her own life and used the letter to frame him.
"The maker of those allegations was not available to be cross-examined, and that's where the trial went awry," Jensen's attorney, Daniel Stiller, said.
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The trial judge argued the letter should be presented to the jury because it did not violate Jensen's Sixth Amendment right to confront witnesses against him. The trial judge went on to say Jensen forfeited that right because he was responsible for why the witness could not appear.
"Without the words from the grave, this trial and the strength of this case is dramatically different and dramatically lesser," Stiller added.
The state has 90 days to appeal this federal ruling. If it does not, Jensen will be released. Until then, the 54-year-old remains behind bars with his sentence to life in prison now uncertain.
Julie Jensen had told neighbors and a doctor that she believed her husband had never forgiven her for an affair she had years earlier, and that she suspected he wanted to kill her. She told police he was researching poisons on his computer. And there was also the letter.
Julie Jensen died in December 1998, but her husband wasn't charged with killing her until 2002. The case was slowed by a legal debate over whether the letter and the beyond-the-grave accusations could be used in court.
Ultimately, the jury did not believe that Julie Jensen committed suicide. The prosecution's case ran five weeks and the defense took only five days. Mark Jensen did not take the stand in his defense. The jury took four days to deliberate before it rendered a guilty verdict.
The couple had two sons, who were 18 and 13, at the time of Jensen's sentencing.
The Associated Press contributed to this report.