After hours of wiretapped calls between Scott Peterson (search) and his mistress, the former fertilizer salesman appears to become aware he is being taped, according to recordings played for jurors Tuesday at his murder trial.

The jury spent a fifth day listening to calls between Peterson and Amber Frey (search) that were made after Peterson's wife, Laci, disappeared in December 2002.

In the recordings, Peterson often sounded apologetic for lying to Frey about being married, but he also was evasive. Frey made the tapes at the request of police.

In a call Feb. 7, 2003, Peterson tells Frey he will be spending the night in Sacramento and says he will call her the next day from a pay phone. Frey then asks Peterson why he is going to Sacramento.

"I can tell you but not on these phones," he says, in an apparent reference to his calls being monitored. It was unclear whether Peterson knew Frey was taping him.

Authorities hope to show jurors the affair was Peterson's motive for killing his wife and fetus.

Prosecutors allege Peterson killed his wife in their Modesto home on or around Dec. 24, 2002, then drove to San Francisco Bay and dumped her weighted body from a small boat he had purchased weeks earlier. The 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.

His attorneys claim he was framed after the real killer learned of his widely publicized alibi. They acknowledge his affair with Frey but said that being a "cad" doesn't make him a killer.

Frey has testified that she called police after discovering her lover was not only married, but suspected in the disappearance of his pregnant wife.

Frey took the witness stand briefly Tuesday, telling jurors about her first public statement on the case given to the media on Jan. 24.

"I spoke of the relation with Scott and ... and I spoke of my hopes for Laci's safe return, as well," Frey said.

Judge Alfred A. Delucchi (search) said defense attorneys will begin their cross-examination of Frey on Wednesday morning. He also granted a prosecution request that bars the defense from asking about relationships Frey had before or after meeting Peterson unless they were discussed on the wiretaps.

Jurors also heard a taped call from Jan. 25, during which Peterson continues to romance Frey.

"It's incredibly brave. It just shows what amazing character you have," Peterson says to Frey about her media appearance, constantly referring to her as "sweetie."

On another call, Peterson expresses frustration that Laci's family "is accusing me of having something to do with it now."

Amber replies angrily that she even was questioned by a detective about her whereabouts the day Laci vanished.

"How could I not possibly think you have something to do with this, Scott?" Amber asks.

"The only way is that you know me well enough to know I could never do anything like this," Peterson replies. "Amber, it just hurts so bad for you to think I could have something to do with this."

During a Feb. 7 call, Peterson is heard sobbing throughout the conversation, saying "you know I'm not a monster, Amber."