Arias, 32, is charged in the June 2008 death of her lover in his suburban Phoenix home. She says she was forced to fight for her life after Travis Alexander attacked her, but police say she planned the killing in a jealous rage.
On Thursday, she sobbed uncontrollably as a prosecutor relentlessly questioned her about the day of the crime.
It was the most dramatic day of testimony in the widely watched death penalty trial that has captured headlines nationwide for weeks with salacious tales of raunchy sex, betrayal and a bloody killing.
"Ma'am, were you crying when you were shooting him?" prosecutor Juan Martinez snapped.
"I don't remember," Arias replied, weeping.
"Were you crying when you were stabbing him?" Martinez asked.
"I don't remember," Arias said softly.
"How about when you cut his throat, were you crying then?"
Testimony resumes next week after Martinez concluded his cross-examination Thursday.