If Arias is sentenced to death, she would be the fourth woman on death row in Arizona. On Tuesday, she pleaded with jurors to spare her.
She called Alexander's murder "the worst mistake" she had ever made, "the worst thing I've ever done." She couldn't have imagined herself capable of such a grisly crime, Arias told the jury.
"But I know that I was," she said. "And for that I'm going to be sorry for the rest of my life -- probably longer."
Arias was living in Yreka, California, when she met Alexander at a business convention in Las Vegas in September 2006. That November, he baptized Arias into the Mormon faith, a ceremony Arias said was followed by anal sex.
Arias became his girlfriend two months later, she testified. They broke up in the summer of 2007, and Alexander began dating other women.
In June 2008, Alexander missed two appointments, prompting friends to go to his house. They found his naked body crammed in a stand-up shower.
He had been stabbed 29 times in the back and torso and shot in the head. His throat was slit.
After her arrest, Arias told an elaborate lie about masked intruders breaking into Alexander's house and killing him before she narrowly escaped.
Relatives who spoke with police described her as mentally unstable.
The trial, which started in January, has been rife with talk of sex, lies and digital images -- among them graphic autopsy photos.