Scott Peterson (search), on trial for the murder of his pregnant wife, talked incessantly about sex and never mentioned he was married, according to a woman who met him at an agriculture conference and later introduced him to his mistress.

Shawn Sibley testified Wednesday that Peterson told her when they first met that he had "lost" his first love. But most of the conversation that night was about sex.

"We'd be talking about something else and he'd bring up sex," she said. "He did ask me my sexual preferences ... sexual positions ... but he was kind of joking."

Sibley later introduced Peterson to his future girlfriend, massage therapist Amber Frey (search).

Prosecutors claim it was that affair that drove him to kill Laci Peterson (search).

Sibley said she met Peterson at the conference in October 2002 and he told her he hadn't "been successful in finding anyone for himself," and that he was looking for a "long-term relationship with someone."

Sibley said she "freaked" when she learned through an acquaintance that Peterson was married.

She called him and confronted him.

"He kept denying it," Sibley said.

He later called her and left a message on her cell phone.

"Scott's just sobbing hysterically ... He says, 'I'm so sorry I lied to you earlier. I had been married. I lost my wife,"' Sibley recalled.

Peterson persuaded Sibley to let him tell Frey the "truth," that he had been married but his wife died.

Sibley later became so suspicious, she testified, that she used the Internet to find out whether Peterson was married, though she didn't find any information.

"Once we found out that Scott was connected to the missing Modesto woman, Amber immediately called the police," Sibley said.

On cross-examination, defense lawyer Mark Geragos (search) prodded her about the sex talk with Peterson.

"It was a two-sided discussion?" Geragos asked.

"Yes," Sibley replied.

"Is it unusual at conferences for people to drink and say stupid things?" Geragos asked.

"No," Sibley said.

"You ever know married men to act idiotic?" he asked.

"Yes, but I've never known a married man to lie to me about being married," Sibley said.

Geragos replied, "Really?"

Prosecutors allege Peterson, 31, murdered Laci, then weighted her body down with concrete anchors and dumped her in San Francisco Bay on or around Dec. 24, 2002. Scott Peterson was arrested four months after she vanished, when the partial remains of Laci Peterson and her fetus washed ashore two miles from where he said he was fishing.

He was charged with murder and could face the death penalty if convicted.

Defense lawyers say someone else abducted Laci Peterson near their Modesto home as she walked the dog, and held her captive before killing her and dumping her body after hearing Peterson's fishing alibi to frame him.

Proceedings ended shortly before lunch Wednesday and won't resume until Tuesday. Judge Alfred A. Delucchi gave jurors an extended break for the Independence Day holiday weekend.