In a surprise move Wednesday, the judge in Scott Peterson's (search) murder trial postponed the cross-examination of Peterson's former mistress and sent the jury home for the rest of the week because of a "potential development."

Judge Alfred A. Delucchi (search) emerged from a 45-minute closed-door meeting with attorneys and apologized for the delay.

"There's been a potential development in this case that has to be checked out before we can go any further," he told the jury.

Groans could be heard in the packed courtroom.

Peterson's defense attorneys were preparing to cross-examine Peterson's former mistress, Amber Frey (search), and had even set up a big screen with a digital media presentation before the lawyers went behind closed doors.

The judge didn't say what the development was. Lawyers are barred by a gag order from discussing it.

Court officials later announced that Thursday's session would be canceled and the trial will resume Monday with Frey scheduled to be on the witness stand. No reason was given for the cancelation.

Delucchi had sent jurors home early on Tuesday so attorneys could discuss the scope of Frey's cross-examination. The judge ruled defense lawyers could not question her about relationships she had with other men — unless they were mentioned on the wiretapped telephone calls between Frey and Peterson that were played for jurors.

Some that were mentioned included a past relationship Frey had with another married man.

Two weeks ago, Delucchi dismissed jurors for the day after meeting with attorneys, saying, "There's been some newly discovered evidence that requires an investigation on both sides." The details of that delay have not been publicly revealed.

Former prosecutor Michael Cardoza (search), 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."

Jurors have heard 24 recorded calls between Peterson and his lover 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 Laci.

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 (search) 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.

Prosecutors allege Peterson killed his wife, Laci, in their Modesto home on or around Dec. 24, 2002, then dumped her weighted body from a small boat into San Francisco Bay. The badly decomposed remains of Laci Peterson 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 Christmas Eve, the day he reported her missing.

His defense attorneys claim he was framed after the real killer learned of his widely publicized alibi.

Wednesday's development came as a surprise even to Frey's attorney, Gloria Allred.

"It is of course frustrating to Amber because she was ready," Allred said. "Amber has suffered such enormous invasions of privacy."