(CNN) -- The death of actor and comedian Robin Williams has officially been ruled a suicide, the coroner in Marin County, California, said Friday.
Alcohol and illegal drugs were not involved, the statement from the coroner's office said. Prescription drugs were found in "therapeutic concentrations," the statement added.
Williams was found dead in his Tiburon, California, home August 11 from what investigators suspected was a suicide by hanging. He was 63 years old.
The death certificate, obtained by CNN on August 21, says his ashes were scattered off the coast one day later.
Investigators believe Williams used a belt to hang himself from a bedroom door, Marin County Assistant Deputy Chief Coroner Lt. Keith Boyd said at the time.
Williams was sober but struggling with depression, anxiety and the early stages of Parkinson's disease when he died, his widow, Susan Schneider, said in a statement in August.
"Robin spent so much of his life helping others," she said. Whether he was entertaining millions on stage, film or television, our troops on the front lines, or comforting a sick child -- Robin wanted us to laugh and to feel less afraid."
Williams had "a recent increase in paranoia" and was sleeping in a stepson's bedroom because of insomnia and anxiety associated with Parkinson's, according to the coroner's report.
A pathology report released Friday said Williams was diagnosed with Parkinson's disease in November 2013, several years after he first noticed symptoms such as tremors in his left arm and a slowing of his left-hand movements.
Last call made to wife
The coroner's report said his body was found about 11:45 a.m. by a personal assistant, who used a paperclip to open the locked door of the bedroom where Williams had been sleeping. Williams was found in a seated position on the floor of the bedroom with a belt secured around his neck and the other end of the belt wedged between a closet door and door frame.
The actor was wearing black jeans and a black short-sleeve T-shirt, the coroner's report said.
A cellphone recovered from Williams' pants pocket was dead. After recharging the phone, the coroner searched through its texts and emails and found no messages referencing suicide, the report said. The last call on the phone was made the night before to Williams' wife, Susan, and lasted 38 seconds.
In one incident the evening before he died, Williams took several wristwatches and put them into a sock and took them to someone's house for safekeeping, an indication of his paranoia, his wife suggested. Also noteworthy, according to Williams' wife, is that he may have learned of the suicide technique from a movie role in which a character Williams portrayed died from autoerotic asphyxiation.
Grief and remembrance
Williams' death was met with an outpouring of grief and recollections. Friend Billy Crystal paid tribute to him at the Emmy Awards, and later helped Williams' son, Zak, throw out the first pitch before Game 5 of the World Series while Williams' other children watched. Daughter Zelda got a tattoo in honor of her father.
Gilbert Gottfried, another friend, remembered a "generous" man who was welcoming to his fellow comedians.
"To see Robin perform was an experience. He was more than a comedian. He was a comedy force of nature," he wrote on CNN.com.
Ellen DeGeneres, Jimmy Fallon, Conan O'Brien and David Letterman, among others, also paid tribute to the comedian.
Williams' long career was notable for his manic, improvisational comedy and his deeply felt acting performances. He won an Oscar for playing a therapist in the 1997 film "Good Will Hunting." A number of his other films, including "Mrs. Doubtfire" and "Patch Adams," were huge box-office hits.
He was also active in a number of charitable causes and frequently took part in USO tours.
On her Twitter feed, his daughter Zelda remembered her dad with a quote from Antoine De Saint-Exupery's "The Little Prince."
"In one of the stars I shall be living. In one of them I shall be laughing. And so it will be as if all the stars were laughing, when you look at the sky at night. ... You -- only you -- will have stars that can laugh."
CNN's Todd Leopold, Greg Botelho and Dan Simon contributed to this story.