EXCLUSIVE: Radar Reveals Why Rob Reiner's Son Really Snapped One Month After His Parents Were Found Butchered in Bed

Shocking information has emerged about Nick Reiner in the weeks leading up to the brutal murder of his parents, Rob Reiner and Michele Singer Reiner, RadarOnline.com can reveal.

Nick, 32, who at press time had yet to enter a plea and was being held without bail at the Twin Towers Correctional Facility in Los Angeles, reportedly suffers from schizoaffective disorder.

He is said to have changed his medication due to unwanted weight gain a month before the couple were fatally stabbed to death in bed at their Brentwood home.

"Once that happened, he went completely off the rails," an insider close to the situation said.

According to the Mayo Clinic, schizoaffective disorder "is a mental health condition that is marked by a mix of schizophrenia symptoms, such as hallucinations and delusions, and mood disorder symptoms, such as depression, mania, and a milder form of mania called hypomania."

There are two types of schizoaffective disorder: bipolar and depressive. Antipsychotics and mood stabilizers may be used to treat the disorder. The condition can be more difficult to treat if the patient has substance abuse issues.

At the time of the murders, it's unclear whether Nick – who has been to rehab at least 18 times – was using drugs.

Some insiders believed Nick snapped because he had relapsed and wasn't on the correct medication, and allegedly killed his parents in a meth-fueled rage.

"Nick is totally detached from reality," said an insider. "He can't seem to process or comprehend what he's done."

Meanwhile, high-profile attorney Alan Jackson, who formally withdrew as counsel for Nick on January 7, declared his former client "is not guilty of murder" under California law.

Danny Svilar, a Wyoming restaurateur who claimed to share a room with Nick at a luxury $60,000-per-month Malibu rehab facility when they were 15, claimed he "knew" Nick killed his parents when the murders made headlines.

"As soon as I saw that Rob Reiner and his wife, Michele, were murdered, I knew exactly who it was," Svilar confessed before he cast doubt on the possibility of Nick pleading not guilty by reason of insanity.

"I would hate to see Nick try to plead this guilty or not guilty by insanity, when in reality he told me how much he f---ing hated his parents, especially his father," the former acquaintance, who was in rehab for a shopping addiction, added.

Despite Nick's alleged feelings about his parents, Svilar claimed Rob and Michele tried their best to help their son.

"Nick had no sense of gratitude, no sense of appreciation," Svilar claimed. "He was just a f---ing pompous little punk. He just wanted to be out, smoking pot, doing pills, doing whatever, and his family just wanted him to get help."

He then recalled the time Nick turned against him.

"From the get-go, he was pretty welcoming, pretty funny," Svilar noted. "But at the same time, there was this side of him that could just, like, flip."

Svilar recalled one time he "compared him to looking like John Travolta's son who died, and that set him off."

"We had good rapport at first, but then I was like, 'Oh, my God, that's who you remind me of.' It kind of turned ugly after that," he recalled. "He definitely tried to get aggressive with me. He tried to get physical, and then a tech had to step in. He was getting into my face and raising a fist."

Before the falling out, Svilar claimed he and Nick "would talk at night after lights were out, and some of the things that he would say really threw me the wrong way."

"Because I'm a 15-year-old boy in the same room as somebody with a crazy addiction. It was very, very chilling, but also a crazy new experience for me," he added.