"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."
A case packed with twists and turns
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 sex, lies and digital images -- among them graphic autopsy photos that showed Alexander's body.
Now, if the trial continues, some of the same gruesome details of his slaying may be presented again in court.
"Because in order for a jury to actually impose the death penalty, they really need to see the cruelty," criminal defense attorney Ashleigh Merchant told HLN. "And they really need to understand the motives behind this murder and what great lengths she went to -- to actually cover this up."