Prosecutors: Why Scott Killed Laci

Outlining a motive in the Laci Peterson case for the first time, prosecutors alleged in court documents that Scott Peterson's affair with another woman drove him to murder his pregnant wife.

Defense attorneys insisted Tuesday the documents contained "out-and-out falsehoods."

In papers filed Monday, prosecutors sketched the broad outlines of what they believe led Scott Peterson to kill his wife, Laci, citing Peterson's affair with massage therapist Amber Frey and his conflicting statements about it to police.

"The defendant's statements concerning Amber Frey support motive for the murder," prosecutors said.

Jury selection is scheduled to start next week. Peterson, 31, could get the death penalty if convicted.

The documents cite Peterson's "romancing" of Frey in the period before Laci Peterson disappeared on Dec. 24, 2002. Her body and that of her unborn son later washed up along the San Francisco Bay.

During a heated exchange in court Tuesday, defense attorney Mark Geragos called the filing "scurrilous" and "replete with what I consider to be out-and-out falsehoods" designed to grab headlines.

"It looked like it was right out of the National Enquirer," he told Judge Alfred A. Delucchi.

Prosecutors detailed a series of allegedly conflicting statements Scott Peterson made in TV interviews. The documents said he tried to deflect suspicion from himself but ended up coming across "quite strongly, as someone who is lying about his involvement in Laci's disappearance."

Among other things, prosecutors said, Peterson admitted the affair to detectives and later denied it after Frey approached police.

Peterson also claimed that he admitted the affair to his wife and that she was "at peace" with it. But prosecutors said witnesses will testify that Laci Peterson never mentioned the affair.

Investigators also noted that Peterson used the past tense when referring to his wife and unborn son before their bodies were found, abruptly correcting himself.

By Kim Curtis