HILLSBOROUGH COUNTY, Fla. — Mental illness is at the center of the Hillsborough County double murder trial for Nicole Nachtman — and mental Health experts are expected to take the stand today.

• Mental illness at center of double murder trial
• Nicole Nachtman accused of killing parents in 2015
• Defense says she had a psychotic breakdown after years of abuse
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Nachtman, 25, is accused of shooting and killing her mom and stepdad, Myriam and Robert Dienes, at their Carrollwood home in August 2015. She is facing two counts of first-degree murder.

The mental health experts will talk about what led up to Nachtman killing her parents. 

Prosecutors say she shot and killed them to rid herself of difficult, demanding parents.  However, her defense attorneys contend she had a psychotic breakdown following years of abuse. 

On Tuesday, Nachtman's older brother told jurors about the conversation he had with his sister when she confessed to the shooting. 

"And then she got quiet again. And then she says, 'I shot 'em.' I said, 'What?' And she answered, 'I shot 'em. I shot mom and Bob.' And I remember leaning forward...I remember leaning forward on the couch, and saying it again. 'What do you mean you shot mom and Bob? Why did you do that?' Something to that effect. And she just started crying really bad and talking really fast," Msgt. Joseph Carey said. 

Nachtman faces life in prison if found guilty. 

LIVE coverage from the courtroom from Spectrum News Reporter Dave Jordan: