"Your verdict, ladies and gentleman, will determine whether or not Jodi Arias spends the rest of her life in prison or if she is sentenced to be executed," Nurmi said, telling jurors they each had to make their own "moral assessment on what verdict is correct."
He then told the panel they would later hear directly from Arias.
"When you understand who Ms. Arias is, you will understand that life is the appropriate sentence," Nurmi said.
Alexander's sister Samantha later described for the panel how their grandmother, who raised the victim, saw her health fail after the killing and died around the time of jury selection.
"Travis was the glue in our family," Samantha Alexander said. She also recalled her brother's charisma, sense of humor, insight and "huge smile."
"Travis was our strength, our beacon of hope, our motivation," she said through tears. "Our lives will never be the same. . . . We would give anything to have him back."
The trial was inexplicably delayed Thursday afternoon after the judge and attorneys met privately. It is set to resume Monday morning when other witnesses will include Arias' friends and an ex-boyfriend who lived with her for several years in California.
Earlier this week, Arias' attorneys asked to be allowed to step down from the case, but a judge denied the request.
Details about the motion were sealed, but legal experts said Arias complicated efforts for her defense when she gave an interview to Fox affiliate KSAZ minutes after her conviction, saying she preferred death over life in prison.
"I believe death is the ultimate freedom, and I'd rather have my freedom as soon as I can get it," Arias said.
During a closed-door meeting with the judge Tuesday, Nurmi and Jennifer Willmott sought permission to withdraw from the case, according to court minutes released Thursday.
Los Angeles-area criminal defense lawyer Mark Geragos said Arias' attorneys have a conflict of interest with their efforts to keep their client off death row and Arias' assertion that she'd rather die for her crime.