Wilson, who was 40 years old, was pronounced deceased at the Metropolitan State Hospital in Los Angeles County on February 1 ... after officials said he suddenly collapsed, never regaining consciousness.

Stanley's family, however, wasn't buying the explanation ... hiring an attorney who filed three lawsuits against the county in March, accusing them of being deceitful with the truth.

"The County has grossly misrepresented the cause and circumstances of Stanley Wilson Jr.'s death," the attorney said in the court filings at the time.

However, an autopsy conducted on February 4 by the medical examiner in L.A. concluded Wilson Jr. passed away naturally from a pulmonary thromboembolism.

According to the Mayo Clinic, that's a "blood clot that blocks and stops blood flow to an artery in the lung. In most cases, the blood clot starts in a deep vein in the leg and travels to the lung."

The report does mention "red abrasions" to the "forehead, right hand, and right knee" ... but they were described by the doctor as "superficial."

The report says Wilson Jr. was in a prescreening area of the hospital and complained of anxiety before he collapsed. Officials say medics responded to the scene, but unfortunately they weren't able to save Stanley.