Defense lawyers for Joseph Oberhansley, 38, made the request after a prosecution witness mentioned Oberhansley's criminal history and past drug use. Clark County Circuit Judge Vicki Carmichael said the testimony could have prejudiced the jury.
Prosecutors say Oberhansley raped his ex-girlfriend, 46-year-old Tammy Jo Blanton and stabbed her to death after he broke into her Jeffersonville home in September 2014. They also say he ate parts of her body after the murder.
The jury had been selected in Hamilton County, about 120 miles north of Jeffersonville, which is a suburb of Louisville, Ky.
Witness Donna Victoria, a close friend of Blanton's, said on the stand that Blanton didn't call the police after an incident between the couple because she "didn't want him to go back to prison," the Louisville Courier-Journal reported.
She also mentioned a conversation she had with Blanton about Oberhansley's drug use.
"This puts him in great peril," Judge Carmichael said. "A simple admonishment to disregard [the comments] would be insufficient and certainly would not clear the prejudices created by the witness' testimony.”
A new trial date has been set for Sept. 3. A new jury will have to be selected.
The Associated Press contributed to this report.