(PHOENIX) -- Jodi Arias, who has spent an unprecedented 18 days on the witness stand, suffers from post-traumatic stress disorder after killing her ex-boyfriend, and therefore can't remember many of her actions, according to a psychologist.
Arias, 32, has admitted to killing ex-boyfriend Travis Alexander in June of 2008 and lying for nearly two years about it, but insists she killed him in self-defense. Arias has said in a Phoenix court that she has "no memory of stabbing him" and that "June 4 is an anomaly for me."
The jury on Monday will continue hearing from Dr. Richard Samuels, a psychologist hired by the defense, who says that even though Arias admits she shot and repeatedly stabbed Mormon businessman Alexander, she can't remember the crime.
"Memories are not formed in many people who are experiencing acute stress, because, chemically, it just doesn't work," Samuels told the court last Thursday.
Arias is charged with first-degree murder.
Alexander was stabbed more than two dozen times, had his throat slit and was shot in the head before his body was dragged into the shower in his suburban Phoenix home.
The prosecutor wants the jury to believe that Arias' testimony that she has no memory of committing the crime is a lie. He wants Arias put to death for killing Alexander, and plans to attack psychologist Samuels' credibility. He spent much of his career as a sex therapist.
Arias' behavior just before her arrest has also caused a stir. Footage from the police precinct where Arias was being questioned shows her doing a headstand in the interrogation room.
She's on her head for almost 30 seconds while she waits for the detective. While waiting, she also snoops through the trash and sings the song "Here With Me" by pop star Dido.
When the detective returns and tells her that she's about to be arrested, Arias asks whether she can have her purse to do a little primping before her now-infamous smiling mug shot was taken.
"This is a really trivial question, and it's going to reveal how shallow I am, but before they book me can I clean myself up a little bit?" Arias is heard saying on the footage.
Arias could face the death penalty if convicted of murder.
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