Arias, 32, faces either a life sentence or death sentence after being convicted of first-degree murder in the death of former boyfriend Travis Alexander in 2008.
In the second phase of the trial, jurors determined there were aggravating factors in the stabbing, slashing and shooting of Alexander. Arias was placed on a suicide watch immediately after the initial verdict when she said she preferred to die rather than spend the rest of her life in prison.
After Judge Sherry Stephens read instructions to jurors in the penalty phase of Arias' trial Thursday, Travis Alexander's brother Steven told the jury he had been hospitalized for ulcers and separated from his wife following his brother's death, The Arizona Republic reported.
"The nature of my brother's murder has had a major impact on me. It's even invaded my dreams," Steven Alexander said. "I've had nightmares about somebody coming after me with a knife, then going after my wife and my daughter."
Stephens told the jurors their decision on the sentence was binding and not a recommendation.
Court appointed defense attorney Kirk Nurmi told the jury during closing arguments Arias' background and family life could mitigate a finding that the slaying was "especially cruel."
"Make no mistake about it, you [jurors] will determine if she dies or spends to rest of her life in prison," Nurmi said. "Each of you gets to make your own moral assessment."
Arias said she killed Alexander in self-defense, but during the four-month trial, Prosecutor Juan Martinez convinced the jury Arias drove to Alexander's house intending to kill him.
The two had sex and took nude photos of one another until Arias attacked Alexander with a knife. She stabbed him 27 times, slashed his throat, and shot him in the head with a handgun she brought with her, evidence showed.