Oscar winning actor Robin Williams' death in August has been officially ruled a suicide, Marin County authorities said on Friday following an investigation and toxicology tests on the comedian's body.

The 63-year-old Williams, whose body was found on Aug. 11 by a personal assistant at his home in Tiburon in the San Francisco Bay area, died of asphyxia due to hanging, the Marin County Sheriff's Office said in a statement. That was the same finding sheriff's officials made in their preliminary conclusion.

Williams was suffering from the early stages of Parkinson's disease and from severe depression, his widow, Susan Schneider, said soon after his death. He had not been ready to share his diagnosis with the public, she said.

A toxicology test on Williams' body revealed the absence of alcohol or illicit drugs in his system, and prescription medications were detected in concentrations consistent with their use for therapeutic purposes, the statement from the Marin County Sheriff's Office said on Friday.

Williams, who was one of the world's most famous stand-up comedians, earned an Oscar for his role in the 1997 drama "Good Will Hunting." He also starred in the comedies "Good Morning, Vietnam," "Mrs. Doubtfire" and "Night at the Museum."