The penalty phase of the Jodi Arias retrial heated up again on Thursday when a psychologist took to the stand to testify on the convicted killer's mental state.

On day 35 of the sentencing retrial, the psychologist and prosecution expert Dr. Janine DeMarte asserted that Arias did not have post-traumatic stress disorder. According to Steve Krafft of Fox 10 News, the psychologist diagnosed her with borderline personality disorder instead; Krafft captured the exchange on his Twitter account.

"Borderline personality disorder is also a mental illness," defense attorney Kirk Nurmi said.

"Yes," DeMarte said in response.

According to Krafft, DeMarte's response was a "significant admission." He reported that she referred to Arias as a "stalker" who was "jealous and manipulative."

"Prosecutor Juan Martinez called the expert witness after a parade of defense witnesses," Krafft wrote. "The prosecutor is trying to convince the jury that Arias deserved the death penalty for the murder of her ex-boyfriend Travis Alexander."

According to Phil Benson of CBS 5 AZ, DeMarte was the state's key witness. The admission that she made in regards to the mental health of Arias could be significant, according to Jen Wood of Jen's trial diaries.

"It's good for the defense because maybe they can get one person on the jury that thinks 'I don't know if I can give somebody with mental illness the death penalty,'" Wood said. "That puts something in the jurors' minds to think about."

The defense team portrayed Arias as a victim of Travis Alexander, who she claimed was emotionally abusive to her. However, DeMarte did her best on Wednesday to tear down that impression in court, according to Krafft.

"Jodi Arias had cordial relationships with men she dated who broke up with her, Dr. DeMarte admits," Krafft wrote on Twitter. "[This] refutes [prosecution's] claim [that] Arias stalked exes."

Krafft reported that defense experts painted Travis as the portrait of a man who used Arias for sex, had an obsession with pornography, and played cruel games with her emotions. DeMarte attempted to tear down that perception as well.

"Dr. DeMarte painted quite a different picture, patiently describing Arias as an insanely jealous stalker who had borderline personality disorder, fixated on Travis, and couldn't let go, spying on him, confronting other girls he dated, and prone to manic episodes of extreme happiness and despair," Krafft wrote.

According to Benson, several court watchers indicated that the defense scored "major points" in the latest developments of the retrial. However, it remained unknown whether or not the psychologist's admission will play a role in the sentence.

Arias was originally convicted of the first-degree murder in regards to Alexander's death back in 2013. A new jury in this retrial is trying to determine whether she should be executed or spend the rest of her life in prison.