Judge Edward Burmila told the Joliet courtroom Thursday he had received a letter from a prison inmate linking the case to the assassination of Abraham Lincoln and the George Zimmerman case, the Chicago Tribune reported.
The inmate asked the judge to communicate with him for more information.
"I won't be communicating with him," Burmila said dryly, as those in the room laughed.
That may have been the only moment of levity amid the grim testimony surrounding the 2004 death of Kathleen Savio. On Wednesday, the judge allowed the prosecution to introduce hearsay comments from Kristen Anderson, a friend of Savio's.
Prosecutors had tried for two years to get the judge to admit hearsay testimony from Anderson and others.
Anderson said Savio told her about five months before she was found dead in an empty bathtub that Peterson had broken into her Bolingbrook house, held a knife to her throat and told her "I could kill you and make it look like an accident."
A coroner later ruled that Savio had drowned.
Peterson is charged in the death of Savio, his third wife, and is the prime suspect in the disappearance of his fourth wife, Stacy Peterson.