The panel began its work Wednesday afternoon, considering charges that Peterson killed his wife, Laci, and in the process, their unborn child, on Dec. 23 or Dec. 24, 2002.
Judge Alfred A. Delucchi gave the jury about 45 minutes of instructions and jurors then met for four hours before breaking for the day.
CBS News Correspondent Tim Ryan reports the jury is sequestered and will remain so until there is a verdict - with over a dozen deputies assigned to watch jurors to make sure there are no irregularities to derail the trial.
No one is expecting an early verdict - although anything is possible - as jurors weigh the evidence of five months of testimony and nearly 200 witnesses.
Jurors have two choices should they decide to convict - first-degree murder, carrying a possible death sentence or life without parole, and second-degree murder, carrying two sentences of 15 years to life.
"First-degree murder you need two things, expressed malice and intent to kill and premeditation," Delucchi told jurors. "Then you also have second-degree murder," a lesser charge the judge added after finding there was ample evidence to support a case that did not involve premeditation.
Prosecutors claim Peterson strangled or smothered his wife and then dumped her weighted body into San Francisco bay. Her badly decomposed remains and those of the fetus washed ashore four months later. Defense lawyers claim someone else abducted and killed Laci and went on to frame her husband for the crime.
"You can't base a reasonable doubt on an unreasonable interpretation of the evidence," prosecutor Rick Distaso told jurors in a brief rebuttal Wednesday to the defense closing argument. "It's just not reasonable that anyone put that body in the bay to frame him. If it's not reasonable, you must reject it."
Winding up closing statements Wednesday morning, the defense lashed out at the notion that Laci Peterson's fetus died in her womb. Defense attorney Mark Geragos reminded jurors authorities never found the placenta or the fetus' umbilical cord, leaving little evidence to determine whether the male fetus was born alive and killed later.
If the fetus died later, Geragos said, "it's not Scott Peterson who did that."
The trial began with jury selection in March, and opening statements were in June.
Geragos has argued the fetus was born well after Laci Peterson vanished, proving his client couldn't be the killer given the intense police surveillance of him in the days and weeks after she disappeared.
A prosecution witness testified the fetus likely died around the same time Laci was reported missing. A defense witness countered that the fetus could have been born weeks later.
"Was that baby wrapped in some kind of plastic? ... We don't know," Geragos told jurors. "The fact of the matter is, though, that that baby looks like it had something wrapped around it to protect it."
Prosecutors have argued the fetus wasn't as badly decomposed as Laci's body because it had remained in her womb for months before being expelled from her decaying body.
Geragos conceded all along that the former fertilizer salesman, who was having an affair at the time Laci vanished, is a liar and a cheat. But he said he shouldn't be convicted of murder.
"You're not supposed to just decide this case on whether or not you like Scott Peterson," he told jurors.
In their closing arguments, prosecutors made their case for premeditation, contending each bit of evidence is like a piece of a puzzle that when put together points to murder. Geragos countered that with so many missing pieces, jurors must decide there is too much reasonable doubt to convict.
Another legal analyst, Dean Johnson, tells CBS News that the prosecution did appear persuasive in final arguments to the jury.
"The last thing the jury heard," says Johnson, "was a powerful rebuttal by the prosecution: 'Why did those victims' bodies wash up where Scott Peterson was fishing?'"
"It's either a frame-up," says Robert Talbot of the University of San Francisco School of Law, who has been observing the trial, "or he did it."
"And the frame-up," says Talbot of the main theory offered by the defense, "just doesn't make any sense at all."