(CBS) - UPDATE: (AP) --
Sheriff's officials say Robin Williams' personal assistant found him with a belt around his neck at his San Francisco Bay Area home.
Marin County Sheriff's Lt. Keith Boyd also said Tuesday that superficial cuts were found on Williams' wrist and a pocket knife was found nearby.
Toxicology results on whether Williams had any drugs or alcohol in his system are weeks away.
Sheriff's officials said Monday a preliminary investigation determined the cause of death was suicide due to asphyxia. Williams was 63 and had suffered for years from periodic bouts of substance abuse and depression.
Williams' press representative Mara Buxbaum said the actor had been battling severe depression recently. Just last month, Williams announced he was returning to a 12-step treatment program.
Coroner's officials say he was last seen alive at home around 10 p.m. Sunday.
The actor and comedian Robin Williams was found dead today at his home in Tiburon, California. Police say it appears to have been a suicide. Williams was 63 years old.
Williams first rose to fame from the stand-up comedy circuit in the 1970s, with a manic improvisational style all his own. He appeared on the sitcom "Happy Days" and then starred as a lovable alien on its popular spin-off, "Mork & Mindy," from 1978 to 1982.
Williams went on to prove he had serious acting talent as well. He delivered critically praised performances in films like "Good Morning, Vietnam" (1987), "Dead Poets Society" (1989), "Awakenings" (1990), and "Good Will Hunting" (1997), for which he won an Academy Award for Best Supporting Actor.
He was a comic whirlwind as a cartoon genie in Disney's "Aladdin" (1992) and "Mrs. Doubtfire" (1993).
Williams also won three Golden Globes, for "Good Morning, Vietnam," "Mrs. Doubtfire" and "The Fisher King."
In his most recent TV series, "The Crazy Ones," which aired on CBS last year, Williams played a quirky genius who ran an advertising agency with his daughter, played by Sarah Michelle Gellar.
Despite all the laughter on screen, his personal life was often troubled. He acknowledged drug and alcohol problems in the 1970s and '80s and was among the last to see John Belushi before the "Saturday Night Live" star died of a drug overdose in 1982. He went through two highly publicized divorces.
More recently, Williams spoke about the fact that he had been drinking again and entered rehab. But he rebounded well enough to joke about it during his recent tour. "I went to rehab in wine country," he said, "to keep my options open."
Born in Chicago in 1951, Williams would remember himself as a shy kid who got some early laughs at home by mimicking his grandmother. He joined the drama club in high school and studied acting at Juilliard, where he had several classes in which he and Christopher Reeve were the only students and John Houseman was the teacher.
Encouraged by Houseman to pursue comedy, Williams identified with the wildest and angriest of performers: Jonathan Winters, Lenny Bruce, Richard Pryor, George Carlin. Their acts were not warm and lovable. They were just being themselves.
"You look at the world and see how scary it can be sometimes and still try to deal with the fear," he told the AP in 1989. "Comedy can deal with the fear and still not paralyze you or tell you that it's going away. You say, OK, you got certain choices here, you can laugh at them and then once you've laughed at them and you have expunged the demon, now you can deal with them. That's what I do when I do my act."