The defense attorney for 15-year-old Carly Gregg says their client deserves a new trial because she was previously treated for hearing voices using horse therapy.

In Sept., a jury in Rankin County, Mississippi, found Gregg, 15, guilty on all counts, and prosecutor Kathryn Newman said Gregg had shown "zero remorse."

The teen was charged with murder and aggravated assault in the March 19 shooting that killed her mother, 40-year-old Ashley Smylie, and wounded her stepfather, Heath Smylie. She was also charged with tampering with evidence for hiding a security camera after the shooting. 

On the first and second counts, Gregg was sentenced to life in prison. On the third count, she received 10 years.

TEEN KILLER CARLY GREGG SENTENCED TO LIFE IN PRISON FOR GUNNING DOWN MOTHER AFTER SHOCKING VIDEO SURFACED

During her initial court appearance, Carly Gregg pled not guilty to the charges. Her bond was set at $1 million. She is being held in the Rankin County Adult Detention Center. (Rankin County)

Viral footage, shown in the trial, showed the chilling moments when the teen opened fire on her mother.

Now, Gregg's defense said that the teen's father revealed that she was "placed in equestrian therapy as a young child due to experiencing auditory hallucinations."

"This new information supports Dr. Clark’s diagnosis of unspecified schizophrenic disorder and is likely to lead to a different result at a new trial," the defense said. "As such, Carly is entitled to a new trial."

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The defense argued that the "undisputed evidence" of the circumstances leading up to Gregg's action should result in a mistrial.

"The undisputed evidence at trial of Carly’s mental illness, loving relationship with her mother and stepfather, absence of prior criminal charges, absence of prior violence, good school record, maternal family support, community support, the victim’s testimony that Carly was not in her right mind and did not recognize him at the time of the offense, and the State’s admission to an absence of motive to commit the alleged crimes do not support the verdict or sentence in this case," the defense wrote.

MISSISSIPPI TEEN MURDER SUSPECT CAUGHT ON CAMERA IN CHILLING FOOTAGE AFTER ALLEGEDLY KILLING MOTHER

"Therefore, this matter calls for a new trial, or in the alternative, a judgment notwithstanding the verdict," they said.

The footage showed Carly Gregg moments after she allegedly opened fire and killed her mother in March 2024. (YouTube/ Law&Crime Trials)

Judge Dewey Arthur disagreed in a decision, saying that no information revealed warranted a new trial.

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"This Court specifically finds that no new and material [sic] has been discovered which probably would produce a different result at trial and, by reasonable diligence, this evidence could not have been discovered sooner," Arthur wrote.

"The Court reviewed the statements and finds these statements would not have probably produced a different result at trial," he said.