CENTENNIAL, Colo. -- The fate of a man convicted of murdering two people is now in the hands of the jury.

The Arapahoe County jury deliberated for a half-hour Friday before it was dismissed for the weekend. The jurors will return Monday morning to decide whether or not to sentence 23-year-old Sir Mario Owens to death.

The panel would have to vote unanimously for Owens to be executed, or he would automatically be sentenced to life in prison.

The same jury found Owens guilty in May of first-degree murder in the June 2005 deaths of Javad Marshall-Fields and Marshall-Fields' fiancee, Vivian Wolfe.

Jurors have already ruled that Owens' case meets all five aggravating factors necessary for the 23-year-old to be eligible for the death penalty.

Marshall-Fields had been set to testify against Owens in another shooting death.

Prosecutors argued that the murder of a witness warrants the death penalty, saying the crime "strikes at the very heart of the justice system."

Prosecutor John Hower argued the murders had a big impact on society and said society should not get to the point where people view a subpoena to testify as the equivalent of a death warrant.

"The killing of a witness cannot be tolerated. It will lead to a world where we no longer live under the rule of law. We live under the code of the street -- you snitch, you die," Hower said.

Hower told the jury that Owens was a "stone cold killer" who never expressed remorse for his crimes. He said "the sweet kid" Owens' family members described had disappeared long ago.

"Somewhere along the line, little Mario ceased to exist ... The killings he committed forfeited the right to live," Hower said.

Defense attorney Daniel King pleaded for mercy, saying prosecutors had been motivated by vengeance, not justice.

"Mercy is not deserved. Mercy is an opportunity, a gift given out of hope," King said.

He also described "mitigating factors" in Owens' life, which was filled with poverty and crime. The defense also claimed he an abnormal brain scan and had development problems. His father was addicted to drugs, King said.

King is looking for just one juror to say "no" to the death penalty. He looked at them individually and told them not to be convinced by everyone else in the panel. Go with what your gut tells you; go with what you believe is right, King told the jury.

The slayings happened three years ago this month, the victims' family members said they had waited a long time to tell jurors about their loved ones.

Fields' grandmother, Sylvia Marshall, told jurors "the whole house went crazy after the murder" and that "it is still not the same." In her words, "everything stopped."

Fields' mother, Rhonda, broke down when she testified. Fighting off tears, she said she misses everything about her son.

She added, "I never in my life believed I would have to bury my son."

Closing arguments in the penalty phase of the trial concluded Friday afternoon. The prosecution and defense each had two hours for their closing arguments and 10 additional minutes for rebuttal.

Colorado has only one person on death row -- Nathan Dunlap. He was convicted of killing four people at a Chuck E. Cheese restaurant in Aurora in 1996.