A prosecution investigator admitted Wednesday that he once suspected there was more than one person involved in Laci Peterson's disappearance and that Scott Peterson's (search) former mistress may have participated.

Steven Jacobson (search) spent most of the morning discussing wiretaps of Peterson's telephone calls in the weeks after his pregnant wife vanished. But on cross-examination, the tone of questioning became heated as defense lawyer Mark Geragos (search) pointedly asked the investigator about details he included in affidavits written to secure warrants for the wiretaps.

"One of the reasons you wanted to get a wiretap is because you believed there were co-conspirators in this case?" Geragos asked.

"Yes sir," Jacobson replied.

"Because you believed that the abduction of Laci Peterson could not" have been done by one person? Geragos prodded.

"I believed that there could possibly have been more than one person involved in Laci's disappearance," Jacobson replied.

Jacobson even wrote in one of the affidavits that "there was no way one person could have done that to Laci Peterson."

During two days of cross-examining Peterson's mistress, Amber Frey (search), Geragos accused her of not fully cooperating with police as she taped hundreds of phone calls between her and Peterson. She denied the allegations and stated that all calls between the pair were taped and handed over to police.

On Wednesday, Jacobson acknowledged that police at one time suspected Frey may not have been recording all of her conversations with Peterson and may even have been involved.

"I don't know if I would label her a co-conspirator. I wanted to listen to more (of the wiretaps) ... I wanted to hear for myself," Jacobson said.

Prosecutors allege Peterson killed his wife in their Modesto home around Dec. 24, 2002, then dumped her weighted body from a boat into San Francisco Bay. The remains of Laci Peterson (search) and the couple's unborn son washed up a few months later, not far from where Peterson claimed he had gone fishing.

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

Frey has never been accused of any wrongdoing.

Earlier in the day, prosecutors played for jurors a series of secretly recorded phone calls in which police say Peterson lies to friends and family and, during one call, inquires about selling his home within weeks of his pregnant wife's disappearance.

In one call, Peterson tells his mother he is in Fresno even though his cell phone records show he was in the Berkeley area, about 185 miles north, said Jacobson.

Prosecutors have suggested Peterson frequented the Berkeley marina to make sure his wife's weighted body had not surfaced. The defense says he was merely checking up on the investigation.

Peterson also called a real estate friend on Jan. 22, 2003, to inquire about selling his furnished home. "I want to talk to you about, you know, selling the house," Peterson says. "You know, but keep it quiet, obviously ... I mean there's no way if Laci comes back that we're gonna stay there."

"Can I sell it furnished?" Peterson then asks.

In other calls played for jurors, Peterson learns about a possible sighting of his missing wife in Longview, Wash., and hears that police there are investigating the tip and viewing videotapes from a store.

"Did Mr. Peterson make any call to the Longview Police Department?" prosecutor Rick Distaso asked.

"No sir," Jacobson said.

But in a Jan. 30 call, Peterson tells a friend he had talked to authorities in Longview.

"I talked to this guy and he's ... he said they were getting the tapes together to look at it," Peterson says. "We're praying it's her."

On several calls, Peterson can be heard talking to Frey, telling her he is preparing to go to Washington to learn more about the possible Laci sighting.

"It's obviously worth any effort, if there's a chance," Peterson tells Frey.

On a Feb. 3 call, Peterson finally speaks with a detective in Washington, who tells him the tip was bogus and he should contact Modesto police for more information.