Nick Reiner believes he is the victim of a conspiracy after his parents’ murder

Nick Reiner knows he killed his parents, Fly And Michele Reinerbut he doesn’t understand why he’s in jail… sources with direct knowledge tell TMZ.

TMZ has a documentary…”TMZ Investigates Reiner Murders: What Really Happened” – airs tonight on FOX and streams Saturday on Hulu. Our sources say Nick is delusional and believes the people who put him behind bars are engaged in a “conspiracy” against him.

Our sources say Nick’s fatal mental spiral occurred about a month before the murders, when doctors changed medications he suffered from schizoaffective disorder, a serious mental illness that causes delusions, hallucinations and mania. The medications made him increasingly dangerous and erratic. We are told that the medications still do not work properly.

We know that Nick’s team was proceeding on the path to pleading guilty because of madness. The point is…this plea does not require proof that a defendant like Nick didn’t know the difference between right and wrong. The key is whether he understood the “character and quality” of his actions. Even if the murders were premeditated, it is possible that a jury could reach a verdict of not guilty by reason of insanity.

“TMZ Investigates the Reiner Murders: What Really Happened” airs Friday night on FOX at 8:00/7:00 p.m. Central and Saturday on Hulu.