REDWOOD CITY, Calif. —  Amber Frey (search), Scott Peterson's (search) former mistress and the prosecution's star witness in Peterson's double murder trial, may take the stand Tuesday.

But the court may first take time to resolve recently discovered evidence that defense attorneys say is "potentially exculpatory."

The judge last week declared a two-day halt to the case so defense attorneys could investigate the evidence, which defense attorney Mark Geragos (search) said could point suspicion away from his client.

Judge Alfred A. Delucchi granted the defense request for a delay after emerging from a closed-door meeting with attorneys on Thursday.

"There's been some newly discovered evidence that requires an investigation on both sides," Delucchi told jurors. "We can't go further until this situation is resolved."

Geragos said last week that preliminary test results on the evidence could be available Tuesday, the same day Frey was set to take the witness stand.

Prosecutors have sought to show the affair, and hopes for financial gain, were Peterson's motives to murder his pregnant wife, Laci.

Lydell Wall of the Stanislaus County Sheriff's Department testified last week that he examined five hard drives from computers seized from Peterson's home and office.

Wall said he found that Peterson searched sales ads for used boats on Dec. 7-8, 2002. He also searched numerous Web sites for fishing information, currents in San Francisco Bay and details on boat ramps in the area.

Prosecutors allege Peterson killed his wife in their Modesto home on or around Dec. 24, 2002, then drove to the bay and dumped her weighted body from a small boat he had purchased just weeks earlier. The badly decomposed remains of Laci Peterson (search) and the couple's fetus washed ashore in April 2003, not far from where Peterson said he launched a solo fishing trip the day she vanished.

The Dec. 7 date could be integral because Shawn Sibley, the woman who set Peterson up with Frey, testified earlier in the trial that she confronted Peterson on Dec. 6 after learning he was married. He had told her he "lost" his wife.

Prosecutors appear to be trying to show that Peterson began hatching the murder plot a day later. Defense attorneys contend it is ridiculous to think Peterson would kill his wife to be with a woman he had only known for several months.