ELKHORN - Dr. Mary Mainland, the Kenosha County Medical Examiner, testified that she knew Julie Jensen died of ethylene glycol poisoning. Mainland says based on the amount of ethylene glycol found in Julie's system, she believed Julie had been murdered. Mark Jensen, 48, is charged with first-degree murder in the death of Julie Jensen, who was found dead of poisoning in 1998 at her home in Pleasant Prairie, a suburb of Kenosha just north of the Illinois border. Mainland believes that if Julie Jensen had killed herself, a larger amount of ethylene glycol would have been found in her body. Dr. Mainland also found internal bruising on Julie Jensen's buttocks, neck, and ribcage. The bruising led Mainland to believe that Julie Jensen could have been asphyxiated, but she couldn't prove it. That is, she says, until a letter from Mark Jensen's cell mate Aaron Dillard surfaced. Dillard wrote a letter to his attorney about a conversation that he had with Jensen in jail. Special prosecutor Robert Jambois read part of the letter in court Friday. "Then he got on top of her, pushed her neck into the pillow, and she died,” Jambois read. Mainland says although Dillard is a career criminal, his letter is believable because he knew details about the case that were not known to the public. The defense says Julie Jensen took the ethylene glycol herself because she was depressed and committed suicide. The defense also says that Aaron Dillard's testimony can't be believed because he made the story up to help him get out of jail sooner. When inmates cooperate in cases, and testify against other inmates, many times they receive reduced sentences.