A man in Wisconsin was found guilty by a jury on Thursday of first degree murder in the poisoning and suffocating death of his wife, who left behind “a haunting letter.”

Mark Jensen, 48, received a mandatory life prison sentence and is eligible for parole if the judge determines so at the sentence hearing.

The jury of seven women and five days deliberated for three days, almost 32 hours, before coming with the verdict on Thursday.

Jensen was revoked bail.

On December 3, 1998, Julie Jensen, 40 was found dead at her home after feeling sick for days.  

In 2002 Mark Jensen was charged with first degree murder in the case of her death, but due to legal evidence the trial was delayed for many times.

After the verdict, prosecutor Robert Jambois said: “I think what Mark Jensen did is the most unspeakable offense I can truly recall. That's one of the reasons it took so long to bring this case to justice. It took a long time to uncover the lies and the machinations of Mark Jensen,” CNN reports.

Among the evidences was a letter written by Julie and given to a neighbor where she accuses her husband for any harm she might suffer. Also there were her statements to police and her son’s teacher saying that she suspects her husband of trying to kill her.

The jurors said that the letter offered them "a clear road map" to conviction.

Mark Jensen was having an affair at that time with a woman he is now married to.

Julie wrote in her letter:  "I pray that I am wrong and nothing happens, but I am suspicious of Mark's suspicious behaviors and fear for my early demise," the Associated Press reports. She said if anything should happen to her the letter must go into police hands.

Defense attorney Craig Albee said: "I'm convinced the jury reached the wrong decision. I'm hopeful that Mark will get a new trial."

Jambois said that Jensen planned to kill his wife and used the internet to search information on ethylene glycol which is commonly used as antifreeze. He gave her sleeping pills and juice with the toxic chemical.

As he saw that her health was improving he decided to suffocate her, pushing her face in a pillow.

The prosecution’s case relied mostly on jail inmates who allegedly heard Jensen in prison saying that he planned to kill his wife, a prison expert who made a mistake in his research and witnesses with faded memories from 10 years ago, the defense claims.

The defense called Julie’s doctor who said that she was depressed and frantic, after he saw her a few days before her death.