Robin Williams at the 2013 Emmys

Robin Williams speaks onstage during the 65th Annual Primetime Emmy Awards held at Nokia Theatre L.A. Live on September 22, 2013 in Los Angeles, California. 

Kevin Winter/Getty Images

The four-time Oscar nominee was found unconscious in his Northern California home on Monday.

Robin Williams died of an apparent hanging Monday, Marin County police said at a Tuesday press conference.

The preliminary cause of death is asphyxia due to hanging, Lt.Keith Boyd told the media.

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Williams was found hanging, with a belt around his neck and rigor mortis had set in, Boyd said. Williams was found clothed, slightly suspended in a seated position, Boyd added, noting that the actor was found by his assistant.

Boyd also said that there's still an ongoing investigation into Williams' death and that toxicology tests will be conducted, which could take a few weeks.

Williams' publicist, Mara Buxbaum, told The Hollywood Reporter Monday that the actor, "has been battling severe depression of late. This is a tragic and sudden loss. The family respectfully asks for their privacy as they grieve during this very difficult time."

Williams was a four-time Oscar nominee who won the best supporting actor trophy for his role in Good Will Hunting. He most recently starred in CBS' one-season comedy The Crazy Ones, alongside Sarah Michelle Gellar.

This article first appeared on The Hollywood Reporter.