Peterson is charged in the murder of his third-wife, Kathleen Savio, whose body was found in a bathtub in 2004. Originally ruled an accidental drowning, the case was reopened when Peterson's fourth wife, Stacy Peterson, disappeared in 2007.
Friday's witness, Scott Rossetto, was a friend of Stacy Peterson's. He spoke about two conversations he had with Stacy before she went missing. Rossetto was going to testify that Stacy told him Peterson forced her to lie about where Peterson was the night Savio died to provide Peterson an alibi.
But Rosetto's story constantly changed and he could not accurately remember the dates he had the conversations with Stacy Peterson. That led the defense to object to his testimony.
"Scott Rossetto comes forward and tells the same story three or four different ways. It happens at different times, it happens at different places," defense attorney Steve Greenberg said.
Will County States Attorney James Glasgow appealed to the judge not to toss out the testimony, blaming the mistake on his office because the team is ill.
Judge Burmila sided with the defense.
Outside the courtroom, Rossetto said he was frustrated his testimony won't be allowed because he couldn't remember exact dates, and could no longer "help" his friend, Stacy. Stacy is still missing.
"It shows that Drew told Stacy to be his alibi, which what really happened that night Stacy confessed to Rossetto is going to be very important," Pam Bosco, Stacy Peterson family spokesperson, said.
Savio's doctor also took the stand on Friday. He said that although she was diagnosed with a form of vertigo that can make people feel unstable on their feet, the chances of her falling in her tub were unlikely.
Peterson is a suspect in Stacy's disappearance, but has not been charged. He maintains his innocence in both cases.