Authorities said Alexander fought for his life as Arias attacked him in a blitz, but he soon grew too weak to defend himself.
"Mr. Alexander did not die calmly," prosecutor Juan Martinez told jurors in opening statements.
Arias said she recalled Alexander attacking her in a fury after a day of sex. She said Alexander came at her "like a linebacker," body-slamming her to the tile floor. She managed to wriggle free and ran into his closet to retrieve a gun he kept on a shelf. She said she fired in self-defense but had no memory of stabbing him.
She acknowledged trying to clean the scene of the killing, dumping the gun in the desert and working on an alibi to avoid suspicion. She said she was too scared and ashamed to tell the truth. However, none of Arias' allegations that Alexander had physically abused her in the months before his death, that he owned a gun and had sexual desires for young boys, were corroborated by witnesses or evidence during the trial. She acknowledged lying repeatedly before and after her arrest but insisted she was telling the truth in court.
Arias spent 18 days on the witness stand describing an abusive childhood, cheating boyfriends, dead-end jobs, a shocking sexual relationship with Alexander, and her contention that he had grown physically abusive.
Psychologist Richard Samuels testified for the defense that Arias suffered from post-traumatic stress disorder and dissociative amnesia, which explained why she couldn't recall much from the day of the killing. Another defense witness, psychotherapist Alyce LaViolette, concluded that Arias was a battered woman.
Their testimony would be crucial to convince jurors that, one, Arias wasn't lying about her memory gaps from the day of the killing, and two, that she did suffer physical abuse by Alexander. Defense attorneys had to get jurors to believe that despite no evidence of Alexander ever having been violent in the past, he had attacked Arias on several occasions, and did so again on the day of his death.