A new "TMZ Investigates" documentary claims that Nick Reiner is currently not mentally fit to stand trial for the alleged murders of his parents, Rob and Michele Reiner.

The special, airing on Fox Nation, reveals troubling details about Reiner's mental health, medication changes, and his behavior while in jail.

According to TMZ executive producer Harvey Levin, Reiner's condition has sharply declined since his arrest.

Speaking on "Fox & Friends," Levin said Reiner is "not competent to stand trial right now" and described him as acting "almost childlike" while incarcerated.

Levin added that Reiner knows what he is accused of doing but cannot fully understand where he is or what is happening to him. "He is out of his head right now," Levin said.

The documentary reports that Reiner had been diagnosed with schizoaffective disorder, a serious mental illness that can cause delusions, hallucinations, and mood problems, Fox22 reported.

About a month before the alleged murders, doctors reportedly changed his medication after he complained about weight gain. Levin said that change "messed Nick up," leading to a rapid mental decline.

TMZ Doc Suggests Drug Use Played Role

The alleged killings themselves are described as extremely violent. Levin called them "incredibly brutal," noting that people in the medical examiner's office were deeply disturbed by the images.

Reiner has been charged with two counts of first-degree murder in the stabbing deaths of his parents.

According to FoxBusiness, the documentary also raises questions about possible drug use at the time of the killings.

Levin claimed the crime had "all the markings of a meth murder" and said Reiner was allegedly using meth after his medication change.

He added that Reiner was arrested in what he described as a drug den. While officials have not confirmed drug use, Levin suggested the level of violence pointed to something beyond Reiner's usual behavior.

"If he were just Nick Reiner without something additional, the carnage wouldn't have been the way it was," Levin said, explaining that investigators believe Reiner was "off the rails" during that period.

The program also discusses the legal strategy expected in the case. High-profile defense attorney Alan Jackson, who previously represented Reiner before withdrawing, has said Reiner is not guilty.

Levin explained that this likely means a plea of not guilty by reason of insanity. "There's no way he'll plead not guilty," Levin said, pointing to Reiner's mental state.