Actor Robin Williams with his daughter Zelda in 2005. Photo: Bill Davila/Reuters

Oscar-winning actor and groundbreaking comedian Robin Williams hanged himself with a belt in his Northern California home after he had sought treatment for depression, a coroner said on Tuesday, based on preliminary findings.

Williams, 63, was found dead by his personal assistant at midday on Monday in a bedroom. He was suspended from a belt wedged between a closet door and a door frame, in a seated position just off the ground, Marin County’s assistant chief deputy coroner, Keith Boyd, told a news conference.

“Mr Williams’s personal assistant became concerned at approximately 11:45am when he failed to respond to knocks on his bedroom door,” Boyd said.

“His right shoulder area was touching the door with his body perpendicular to the door and slightly suspended. Mr Williams at that time was cool to the touch with rigor mortis present in his body,” Boyd added.

The official preliminary cause of death was asphyxia due to hanging, he said, and conclusion of the investigation is still weeks away.

Officials also found a pocket knife near Williams and superficial cuts on his left wrist with dried red material that matched what was on the knife blade. It was not yet known if it was his blood.

Williams had been open about his struggles with alcohol and cocaine and in the past months had entered a rehabilitation centre to help him maintain sobriety. But many questions remained over what could have led him to take his own life.

The entire world is forever a little darker, less colourful and less full of laughter in his absence

Williams’s publicist, Mara Buxbaum, said that he had been suffering from severe depression, and Boyd acknowledged that he had been seeking treatment without giving more details.

Williams was last seen alive by his wife, Susan Schneider, on Sunday night when she retired for the evening. She left the next morning around 10am, thinking that her husband was still asleep.

Boyd would not say whether Williams had left a suicide note, nor if any drugs or alcohol were involved. The full toxicology report would take two to six weeks, he said.

In addition to his wife, Williams is survived by three grown children – daughter Zelda and sons Zachary and Cody.

Zelda, 25, said: “Dad was, is and always will be one of the kindest, most generous, gentlest souls I’ve ever known, and while there are few things I know for certain right now, one of them is that not just my world, but the entire world is forever a little darker, less colourful and less full of laughter in his absence. We’ll just have to work twice as hard to fill it back up again.”

“I lost my father and a best friend and the world got a little grayer. I will carry his heart with me every day. I would ask those that loved him to remember him by being as gentle, kind, and generous as he would be. Seek to bring joy to the world as he sought,” Zachary Williams, known as Zak, said in a statement.

And 23-year-old Cody added: “There are no words strong enough to describe the love and respect I have for my father. The world will never be the same without him. I will miss him and take him with me everywhere I go for the rest of my life, and will look forward, forever, to the moment when I get to see him again.”

Funeral arrangements are pending.

Addiction ‘lays in wait’

Addiction seemed to stalk Robin Williams, tempting him when he was weak and taunting him when he least expected it.

“It waits,” he told Good Morning America in 2006. “It lays in wait for the time when you think, ‘It’s fine now, I’m OK’. Then, the next thing you know, it’s not OK. Then you realise, ‘Where am I? I didn’t realise I was in Cleveland’.”

He battled periodic bouts of substance abuse and depression, opening up about them to journalists with self-deprecating wit.

“Cocaine for me was a place to hide. Most people get hyper on coke. It slowed me down,” he told People in 1988.

One of his first wake-up calls was in 1982 when fellow comedian John Belushi died of a drug overdose. His friend’s passing, coupled with impending fatherhood, forced the comedian to quit cocaine and alcohol.

Sobriety lasted 20 years. Then the taunts became overwhelming again.

The Oscar winner spent several weeks in the Canadian city of Winnipeg in the spring of 2004 filming The Big White, playing an Alaskan travel agent nearing bankruptcy. He told The Guardian in 2010 he felt lonely and overworked.

“I was in a small town where it’s not the edge of the world, but you can see it from there, and then I thought: drinking. I just thought, ‘Hey, maybe drinking will help’. Because I felt alone and afraid,” he told the newspaper. “And you think, ‘Oh, this will ease the fear’. And it doesn’t.”

He told Parade magazine in 2013 that his relapse after two decades of sobriety was frighteningly simple.

“One day I walked into a store and saw a little bottle of Jack Daniel’s. And then that voice – I call it the ‘lower power’ – goes, ‘Hey. Just a taste. Just one’. I drank it, and there was that brief moment of, ‘Oh, I’m OK!’ But it escalated so quickly. Within a week I was buying so many bottles I sounded like a wind chime walking down the street.”

A family intervention persuaded him to seek alcohol abuse treatment at Oregon’s Hazelden Springbrook centre in 2006.

Williams continued his recovery by attending weekly AA meetings. But his second marriage, to film producer Marsha Garces, ended in 2008, largely because of his drinking, even though by then he was sober. Recently, a new bout of depression prompted Williams to enter rehab.

On Monday, the struggle finally ended.