ELKHORN - Did he poison his wife? Or did she commit suicide? That's what a Walworth County jury has to decide. The defense spent several hours trying to discredit one of the prosecution’s key witnesses. The defense attorney says Edward Klug, a former co-worker of Mark Jensen’s, is not a credible man. Attorney Craig Albee says Klug, a key witness for the prosecution, changed his story several times. Mark Jensen and Edward Klug barely knew each other, but Klug testified that his former co-worker told him he planned to kill his wife. "He mentioned Web sites of how to kill your wife, and of poison, etc,” Klug said. Klug says the conversation took place after bar time while the two were wife bashing late one night at a business conference. Klug's testimony wavered throughout the day. Albee says Klug's testimony kept changing because that conversation never happened. “Do you enjoy the attention you’ve gotten since making up these stories about Mark Jensen?” Albee asked Klug. “These are not made up stories,” Klug said. Albee says Klug told other people Jensen planned to kill his wife to get attention. Another reason Albee says Klug made up the story was so his wife wouldn't know he was out with other women. The defense claims Klug read the criminal complaint, learned all about the case, and then came forward to authorities this past year. Edward Klug's wife and an insurance agent also took the stand. The insurance agent testified Mark Jensen was the beneficiary of his wife's $100,000 insurance policy.