The actor was found dead around noon on Monday, at his home in California, by his personal assistant.
The comedy actor struggled with addiction during the 80s, but is believed to have been sober for the past 20 years.
County Sheriff, Lt Keith Boyd said the 63-year-old had been treated for depression before his death.
Although a post mortem examination has determined his cause of death to be asphyxia, they are waiting for the results of a toxicology report before their final ruling.
Since he passed away, tributes have flooded in the Oscar winning actor. In a statement, his wife, Susan Schneider, spoke of her devastation at the loss.
“As he is remembered, it is our hope the focus will not be on Robin's death, but on the countless moments of joy and laughter he gave to millions.”
Earlier today, comedian Jason Manford has paid tribute to late actor Robin Williams, 63, by posting a touching message about the impact of depression.
He wrote: “If you feel alone and down, anxious and low. If you feel deep sadness but can't find a root cause. If people tell you to 'snap out of it' or 'things can only get better' or 'what doesn't kill you makes you stronger', know that it's simply not always true.
“Please seek help. No one will think you're being melodramatic, I swear. No one will think you're silly or wasting people's time. No one will say 'what? But you're always so happy, maybe you're just having a bad day'. For some people, every day is a bad day and they get through it, but sometimes they stop getting through it.”
For anyone who needs advice, please visit the Samaritans websiteor call 08457 90 90 90.
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