Death Foretold: '20/20' Exclusive

Feb. 29, 2008— -- For people on the outside looking in, Julie Jensen appeared to have it all: a successful stockbroker husband, Mark, to whom she'd been married for 14 years, two wonderful sons and a beautiful suburban home on tony Lakeshore Drive in Pleasant Prairie, Wis. "We all looked up to her as being a perfect mother," said friend Kim Shaw.

"[Julie and Mark] would always be outside, always working on some kind of project," remembered her friend and next-door neighbor Margaret Wojt. "Just laughing and having fun with it ... it was amazing to watch them."

But gradually, their marriage started to unravel. Wojt's husband, Ted, told "20/20" Mark had wanted Julie to be more sexually experimental. "She said, 'Aw, [Mark] wants me to be like these other women ... his friends. They go to the bars, three in the morning. They go to the strip clubs ... Drinking ... I'm not that. I don't want it."

Friends say Julie had previously contemplated divorce, but Wojt said Julie told her, "Mark would kill me first, before he divorced me."

Then, on Dec. 3, 1998, 40-year-old Jensen was discovered dead in her bed by her husband Mark. In the early hours of the investigation, police said suicide was the likely cause of death. District Attorney Bob Jambois was at the Jensen house that day and felt differently.

"It didn't look right," he said.

The family quickly held funeral services.

"Mark was standing five feet from her casket laughing and joking and acting like someone at a cocktail party" said Vorwald. Neighbor Carrie Ashley said, "I would probably mourn a stranger more than he mourned Julie."

When the autopsy came in, it did not confirm Jambois' suspicions and found no evidence of foul play. Instead, Jambois said, "It showed nothing."

The Letter

What neither Mark nor the investigators knew was that Jensen had left her own testimonial about what was going on inside her home. Before her death, she gave an envelope to Ted and Margaret Wojt. She told them that "if anything happens, give it to the police."

The Wojts, to whom Jensen had confided, gave police the sealed envelope. In it was a letter written by Julie Jensen, accompanied by a photo of a shopping list. Her words were simple and shocking.

"I am suspicious of Mark's suspicious behaviors and fear for my early demise," she wrote. "If anything happens to me, he would be my first suspect. I would never take my life because of my kids — they are everything to me!"

Jensen also discussed in the letter a possible reason why her husband was harboring hostilities towards her. She referenced a brief affair that she had years earlier and said her husband had "never forgiven me." CLICK HERE to read the letter in its entirety.

The shopping list was written by Mark Jensen and included a list of such items as poisons and syringes. Margaret Wojt's reaction to the letter was a mix of sadness and anger. "I don't think you need anything else. Just read this and you know what happened," she told "20/20."

Investigators viewed the contents of the envelope as key evidence and "as Julie's last will and testament," said Jambois.

Legal Wrangling

Mark Jensen had secrets of his own. He had been having an affair with a married co-worker, Kelly LaBonte, and professed his love to her in emails that were found on his computer.

Could this have been a motive for murder? Prosecutors thought the letter and emails would help prove that Mark Jensen had a hand in his wife's death.

There were months of legal wrangling but eventually investigators were dealt a crushing blow. In 2002, the letter was ruled inadmissible. According to U.S. law, the accused always has the right to face his accuser.

"He can't confront her because he killed her," said an outraged Jambois.

Julie Jensen's four brothers were devastated. "We should fight to get the letter admitted. Because that was Julie's voice," said Paul Griffin, a brother.

In 2007, after years of legal disputes which made their way to the Wisconsin Supreme Court, Julie Jensen's letter was finally ruled admissible and a trial date was set.

The Trial

Mark Jensen was accused of murder in the first degree, and nine years after his wife's death he was the focus of a high-profile trial shown live on cable television and the Internet.

Attorney General Bob Jambois argued that the man poisoned his wife with anti-freeze and then suffocated her so he could start a new life with his mistress. Kelly LaBonte moved into the Jensen household shortly after Julie Jensen's death, and she and Mark Jensen were married in 2002.

The suffocation argument was a shift in the case that came after Aaron Dillard, a jailhouse informant with an extensive criminal record, came forward. Mark Jensen and Dillard were housed together in a Wisconsin jail, and Dillard said the suspect told him that he had fed his wife juice mixed with anti-freeze but that "[Julie] wouldn't die fast enough." Dillard testified that the suspect told him his sons saw their mother having difficulty breathing and "wanted to take her to the hospital. He told me he got scared. And that's when he rolled her over and sat on her back, pushed her face into the pillow."

In his exclusive interview with "20/20" Dillard said Mark told him a different story initially. Mark said "that she [Julie] poisoned herself with antifreeze and she tried to commit suicide, that basically her whole family was crazy, and she followed the same footsteps." But then, Dillard said, "it started spilling out" after Dillard made a comment about how "all of us have some problem in our life."

"He [Mark] was teary-eyed talkin' about his kids. And that's when I ... brought in the point of we all did what we did to get here. And then he ... that's when he came out with and started telling me more about what he did."

According to Dillard, Mark's demeanor during his purported jailhouse confession was unemotional. "He didn't show any sorrow about his wife been [sic] dead. He didn't. About her passing away. About any of it."

At the trial, defense Attorney Craig Albee quickly attacked Dillard's testimony, and got him to admit he was a con-man on the stand. Albee said simply to the jury, "You heard Aaron Dillard is a liar. You cannot believe him beyond a reasonable doubt."

Witness after witness came forward to talk about Julie Jensen's character and when it was time for Ted Wojt to take the stand he told the jury that Jensen believed her husband was trying to kill her. Ted testified that she had seen him "on poison sites" on the Internet. He believed she thought her husband was "trying to make me look crazy, to take my kids." Julie Jensen took her suspicions to the police before she died but, without proof, her husband was not questioned.

Julie Jensen had filed for divorce years earlier but Julie's brother Paul testified that Mark told Julie she would never see their sons again if she went through with it.

Defense attorney Craig Albee told the jury that "facts will prove that Mark Jensen did not kill his wife. Depression and despair caused [Julie] to taken her own life." Albee continued to tell the jury that Julie framed Mark by leaving the letter making it look like he harmed her because "her depression and her despair and her anger and her delusional thinking caused her to point the finger at Mark."

Dr. Richard Borman, Julie's long-time physician, testified that she came to see him days before her death and that he was worried. "She was highly upset. It was burned into my mind. I'd never seen her look like that. She was distraught, almost frantic, actually," he said. Borman said Julie was concerned about her family's previous history with mental illness, particularly her mother's life-long struggle with alcoholism and serious depression. Borman prescribed her Paxil and Ambien.

Life in Prison

Ultimately, the jury did not believe that Julie committed suicide. The prosecution's case ran five weeks and the defense took just five days. Mark did not take the stand in his defense.

The jury took four days to deliberate and before a packed courtroom, the foreman read a verdict of guilty in the murder of Julie Jensen.

Albee said he's "convinced the jury reached the wrong decision" and is "hopeful that Mark will get a new trial."

On Wednesday Mark Jensen, 48, was sentenced to life in prison without parole. Currently he is in jail. In the meantime, Julie's two sons, ages 18 and 13, are being raised by his wife and former mistress.