Jurors determined there were aggravating factors in Arias' 2008 slaying of her former boyfriend.
The determination followed arguments in which prosecutor Juan Martinez said Arias, 32, of Yreka, Calif., knew what she was doing when she stabbed, slashed and shot Alexander, ABC News reported.
"We can imagine the absolute terror as he's sitting there, defenseless. As he's seated the knife comes toward him, is hitting him. That is extreme emotional anguish, mental anguish, to watch the blade come up to him," Martinez said.
Under Arizona law, at least one of several specific aggravating factors must apply for a convicted murderer to be eligible for capital punishment, The Arizona Republic reported.
The finding that the slaying of Alexander was "especially cruel" means the jury can consider whether to sentence Arias to death when it begins the sentencing phase of the trial Thursday. The defense will be able to present evidence about Arias' background and family that could mitigate the finding of cruelty.
Arias' attorneys Wednesday tried to convince the jury Arias was bipolar and had had a "violent outburst" episode when she killed Alexander -- so she could not have known what she was doing. The defense said it was possible Alexander was unconscious after the first stab wound, and could not have experienced any further pain or suffering.
Arias said she killed Alexander in self-defense, but during the four-month trial, 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, court records showed.