Responding to a question from Assistant District Attorney Deborah Ryan, the sergeant said the defendant's father "wanted me to know his daughter could be despicable."
Although the judge had instructed the jury to disregard the remark, defense attorney Matt Nelson argued the statement was so prejudicial his client could not receive a fair trial.
Gavin agreed that "a parent's condemnation of their own child is a damaging indictment." The judge said he regretted that the end of the case will be delayed for all the parties.
"Certainly a retrial is burdensome," the judge said. "But it's a small price to pay to ensure a fair trial."
Prosecutors say the couple attempted to poison Kevin Mengel Jr., 33, on June 17, 2010. They alleged that when the toxin failed to take immediate effect, Shappell fatally bludgeoned his employer with shovels from the landscaping business the Mengels owned.
Shappell, an employee of the company, pleaded guilty last month. He received a 40- to 80-year prison term and will testify against his former paramour when the case is retried.
