The move came after a witness for the prosecution testified that he believes Peterson placed a bullet on his driveway after he helped Kathleen Savio change her locks after she and Peterson had split -- against Peterson's wishes. Peterson, a former Bolingbrook police sergeant, is accused of killing Savio, his third wife, in 2004.
Judge Edward Burmila dismissed the jury after Thomas Pontarelli's testimony about the bullet. Pontarelli was Peterson and Savio's neighbor. He was also there when Savio's body was found in the bathtub in 2004.
Judge Burmila blasted prosecutors for bringing up information that could make the former police officer look bad in the eyes of the jury. He also called a recess.
The state responded that it had not intended to "poison" the jury but wanted to let Pontarelli share his "true feelings" about Peterson.
Prosecutors argued against a mistrial, denying repetitive errors. The judge appeared close to declaring a mistrial Tuesday after a prosecutor began to discuss an allegation that Peterson once tried to hire a hit-man.
Neighbor talks of finding Savio's body
Pontarelli was the first witness called for the prosecution Wednesday, the second day of testimony in the case. He and his wife, Mary, discovered Savio's body in dry bathtub in a fetal position with bruises and blood coming from her head. He also said the bathtub was clean.
Pontarelli said Peterson was in Savio's home when her body was found and he followed them into the bathroom to check for a pulse. Moments later, Pontarelli said Peterson called someone and said "just found [his] wife dead and people will think [he] did it."
Prosecutors say Peterson killed Savio and staged a household accident in an attempt to keep her from collecting a portion of his pension and other assets. The death was initially labeled an accident -- until the case was reopened after Peterson's fourth wife, Stacy Peterson, vanished in 2007. A second autopsy showed Kathleen Savio's death was a homicide.
Peterson is also a suspect in Stacy's disappearance. He denies involvement in either case.
Outside the court house in Joliet, Peterson's attorneys told reporters their client remained relaxed and was pleased with how the trial was going so far. They also reiterated their main defense that Savio's death was just an accident.
"There is no sign that it was anything but an accident. There's no sign of a struggle at all, and that's why I went into how Kathy was well known among everybody that knows her as a real fighter, a person with a lot of spirit, somebody who will never take no for an answer, who always wants to get the last word and always fights for everything. If she was being attacked and someone was trying to kill her, there would be a real sign of a struggle," Peterson defense Attorney Joel Brodsky said.
(The Associated Press contributed to this report.)