Judge Alfred A. Delucchi stopped the trial Wednesday just as Amber Frey, Peterson's former mistress, was set to be questioned by defense attorney Mark Geragos.
"There's been a potential development in this case that has to be checked out before we can go any further," Delucchi told jurors.
Groans could be heard in the packed courtroom.
"The wind came out of that courtroom. All the air was sucked out when Judge Delucchi indicated we were not going forward today," CBS News Legal Analyst Trent Copeland said.
Delucchi didn't say what the development was and lawyers are barred by a gag order from discussing it.
The surprise in the courtroom led to all kinds of speculation as to what could cause the delay, reports Gloria Gomez of CBS affiliate KOVR in Sacramento.
Former prosecutor Michael Cardoza Cardoza, who has been observing the trial, speculated Wednesday's development may influence how the defense questions Frey.
"It has to be some new information that might allow a different subject for cross-examination," Cardoza said. "It's important to Amber's testimony."
The only certainty -- the biggest day in the trial became a big bust.
The delay came as a surprise even to Frey's attorney, Gloria Allred, who said outside court that her client was prepared to testify.
"It is of course frustrating to Amber because she was ready," Allred said. "The delay causes even more of an inconvenience for her and her family ... Amber has suffered such enormous invasions of privacy."
Even Peterson's lawyers appeared to be prepared to move forward with Frey's cross-examination. The courtroom was full of attorneys' friends and family members who had come from as far away as Los Angeles.
Delucchi later canceled Thursday's session without explanation. Court is back in session Monday.
Jurors have heard 24 of hundreds of calls recorded between Peterson and Frey as authorities searched for his pregnant wife, Laci, between late December 2002 and February 2003. Authorities hope to show jurors the affair was Peterson's motive for killing his wife.
Throughout the tapes, Peterson is heard proclaiming his love for Laci while at the same time romancing Frey. He continuously apologizes for lying to Frey about his marriage and begs her to meet with him, even as authorities searched for his wife.
On one call recorded Feb. 10, 2003 — the day Laci Peterson had been expected to give birth to the couple's child — jurors heard Peterson calling Frey "sweetie" and directing her to a location in a parking lot at a hospital near Fresno where Frey found Peterson had left her a bag of birthday gifts.
Peterson is accused of killing Laci in their Modesto home on or around Dec. 24, 2002, then dumping her weighted body from a small boat into San Francisco Bay. The remains of Laci and the couple's fetus washed up along a bay shore in April 2003, not far from where Peterson said he launched a solo fishing trip the day he reported her missing on that Christmas Eve.
The defense claims Peterson was framed after the real killer learned of his widely publicized alibi.