Scott Peterson's fate now rests in the hands of the jurors who convicted him of murdering his pregnant wife Laci.

The jury, who will resume deliberations tomorrow after failing to come to a decision Thursday, must recommend either death or life in prison without parole.

If they do recommend death, the judge can reduce the sentence to life. But he cannot impose death if the jury recommends life in prison.

Earlier Thursday, the defense and prosecution wrapped up their closing arguments in the trial's penalty phase. The judge then instructed the jurors on the penalty deliberations and dismissed them from the courtroom.

Characterizing Scott Peterson (search) as a monster who coldly and methodically plotted to kill his pregnant wife, prosecutor Dave Harris told jurors on Thursday that the only just punishment was death.

On Nov. 12, the jury found Peterson guilty of first-degree murder for killing Laci Peterson (search), and of second-degree murder for her fetus' death.

Prosecutors say Peterson killed Laci in their Modesto home on or around Dec. 24, 2002, then dumped her body into San Francisco Bay (search). The remains of Laci and the fetus were discovered about four months later a few miles from where Peterson claims to have been fishing alone the day his wife vanished.

Harris called Peterson "the worst kind of monster" and undeserving of sympathy in his 40-minute closing argument.

"This is somebody who had everything and threw it away," Harris said, pointing at Peterson seated stiffly at the defense table, intently watching the jury of six men and six women. "He had a plan and he executed it."

Harris also reminded jurors that Thursday marked the anniversary of Peterson's "monstrous plan" to murder his wife.

"Two years ago today, the defendant, Scott Peterson, bought a boat," Harris said. "He told [his mistress] Amber Frey his wife was 'lost.'"

But defense lawyer Pat Harris begged jurors to give Peterson the chance to "do some good for the rest of his life" by sending him to prison without the chance of parole.

In his closing arguments, defense lawyer Mark Geragos told jurors he's been "tormented" by the Peterson case -- and surprised by the guilty verdicts.

"You can't find a more tortured, emotionally charged case than when something like this happens to, what I consider to be, two very fine families," he said.

Defense attorneys called 39 witnesses over seven days in the penalty phase of the double-murder trial. Prosecutors called just four of Laci's family members on the first day, Nov. 30.

"Thirty-nine witnesses," prosecutor Dave Harris said. "And those 39 witnesses pretty much all said the same thing. This man who sits here, this convicted double murderer, is not the man that I know."

Dave Harris walked over to the defense table, stood directly in front of Peterson and pointed at him. "They didn't know the real Scott. ... That he's a manipulator. That he's a liar."

He then showed a television news segment recorded before Peterson was arrested in which he sobbed uncontrollably and talked about how much he missed his wife.

"He played the part of a grieving husband," Dave Harris said. "The great fraud. He turned on tears and played the part. ... He's not a person who deserves your sympathy."

Pat Harris, in his closing argument, told jurors why Peterson doesn't deserve to die.

"We've tried in the last week to put on people from all walks of life — all types of people who knew Scott," he said. "We tried to show you who we believe Scott Peterson is."

He acknowledged to jurors it could be confusing to convict someone of two murders, then be asked to sit and listen to people talk about his good qualities: hardworking, respectful, generous.

Pat Harris stood in front of Peterson, pointed at him and told jurors prosecutors misrepresented him as arrogant.

"That doesn't match him, and you know it," he said, his voice barely audible in the gallery despite being asked by the judge to speak up. "Did he manage to fool all these people?"

Peterson's mother, a frail-looking Jackie Peterson, spent a tearful 40 minutes on the stand Wednesday, urging jurors to sentence her son to life without parole and save the family further pain.

"I really feel that if you were to take Scott away from us ... we would lose a whole family," she said, crying so hard at times she was unintelligible. "It would be like Laci never existed."

She begged jurors to see the good in her son.

Geragos reminded jurors that even if they spare Peterson's life, "He will stay in that cell every single day until he dies."

But Dave Harris said Peterson only has himself to blame for hurting his family.

"The person that's responsible is right there, right there, that's the one that's responsible," he said. "Leaving his wife's body to rot on the bottom of the ocean. Leaving his son to be found as trash in the debris. .... That is not something that should be rewarded by sparing his life."

After the defense's closing argument and instructions from the judge, jurors will be sequestered in a hotel for deliberations.

The Associated Press contributed to this report.