Nick Reiner May Have Been on Meth When He Killed His Parents, '2 Angry Men' Podcast

Nick Reiner's murderous rampage that resulted in the horrific death of his parents may have been fueled by more than mental illness -- meth may have played a big factor.

We sent a camera to Exposition Park near downtown L.A. -- where Nick was arrested -- to ask people about the drug culture in the area, and whether they ever saw Nick there.

One of the people we spoke with -- featured on the most recent episode of the "2 Angry Men" podcast -- said flatly ... Exposition Park is a drug den where users can get anything they want, including meth. He also said Nick looked familiar.

The murders were shockingly brutal -- even to the Medical Examiner's staff as well as law enforcement. Rob and Michele Reiner were butchered -- it was carnage.

Harvey and Mark Geragos go through the markings of a meth murder, with the help of Dr. Drew, who also believes the brutality signals Nick was on a drug like meth.

Geragos says he has recon from the jail where Nick is being housed ... he's almost childlike and doesn't have a clue why he's there.

TMZ broke the story ... Nick had been stable on a drug cocktail for his schizoaffective disorder until a month before the murders, when he complained to doctors the meds had made him gain weight. The doctors changed his meds and he spiraled out of control.