It's a turn in the 13-week old trial that may foreshadow a portion of the defense case that Peterson had nothing to do with the murder of his pregnant wife.
Steven Jacobson, an investigator with the Stanislaus County District Attorney's Office, spent most of Wednesday 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 pointedly asked Jacobson 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 coconspirators 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."
Jacobson is due back on the stand Thursday.
During two days of cross-examining Peterson's mistress, Amber Frey, Geragos accused her of not fully cooperating with police as she taped hundreds of phone calls between her and Peterson. She denie0d 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 was not cooperating fully and may even have been involved.
"I felt it important to either corroborate her statements she was making to police or if she wasn't being truthful with police, to find that out, as well," Jacobson said.
Jacobson said Frey may not have been recording all of her conversations with Peterson.
"I don't know if I would label her a coconspirator. I wanted to listen to more (of the wiretaps) ... I wanted to hear for myself," Jacobson said, adding that authorities met just last week and determined Frey had been cooperating and indeed did turn over all of her tapes.
She is no longer considered a possible suspect.
"Law enforcement was mistaken," Jacobson said. "We were operating under not a valid concern there."
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.
During one call, he tells his mother, Jackie, he is in Fresno. Jacobson testified Peterson was, in fact, in the Berkeley area at the time, according to his cell phone records.
"I cannot think of an innocent explanation for lying about his location and it implies and it infers guilty knowledge about why he was there and the only reason he would have guilty knowledge about being there at the bay is his fear that may discover the body of his wife," legal expert Chuck Smith told CBS News.
Prosecutors have suggested Peterson frequented the Berkeley marina to make sure his wife's weighted body hadn't surfaced. But defense lawyers say he was merely checking up on the investigation.
On Jan. 22, 2003, as police continued to search for Laci, Peterson called a real estate agent friend to inquire about selling his 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?" Distaso asked.
"No sir," Jacobson said.
But later, Peterson tells friends and family he had talked to authorities in Longview.
Jacobson testified that Peterson had not yet made any inquiries with Washington authorities, according to the wiretaps.
"The general point is that innocent people don't lie. If you lie, you lie for a reason," former assistant district attorney Jim Hammer told CBS News.
Prosecutors allege Peterson killed his wife 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 the day he reported her missing.
His defense attorneys claim he was framed after the real killer learned of his widely publicized alibi.