This is essentially what I have read elsewhere:
At the height of his career, Arbuckle was under contract to Paramount Studios for $1 million a year, the first such official salary paid by a Hollywood studio. On September 3, 1921, Arbuckle took a break from his hectic film schedule, driving to San Francisco with two friends, Lowell Sherman and Fred Fischbach. The three checked into the St. Francis Hotel, decided to have a party, and invited several women to their suite. During the carousing, one of the women, a 26-year-old aspiring actress named Virginia Rappe, became seriously ill and was examined by the hotel doctor, who concluded that she was merely intoxicated.
In truth, Rappe had been a sick woman for some time. She suffered from chronic cystitis, which would cause her to become violently ill after drinking alcohol. She was also widely rumored to be a carrier of venereal disease. Significantly, while in San Francisco she allegedly asked Arbuckle to help pay for an (illegal) abortion. In her book Frame-Up!, author and researcher Andy Edmonds theorizes that the after-effects of an illegal abortion may have contributed to Rappe's illness at the party.
Rappe died three days later of peritonitis caused by a ruptured bladder. Rappe's companion to the party, Maude Delmont, tried to blackmail Arbuckle over his involvement in the matter, claiming that he'd crushed Rappe's innards while raping her. Arbuckle, confident he had nothing to be ashamed of, refused to be intimidated. Delmont then made a statement to the police in an attempt to get money from Arbuckle's attorneys, but the matter soon got out of her hands. Newspapers, particularly those controlled by William Randolph Hearst, made a fortune endlessly crucifying Arbuckle in spurious and surreally vicious articles and editorials (the New York Times stated that Rappe was lucky to be crushed to death during the rape before having to consciously endure "a fat man's foulness").
Roscoe Arbuckle's career is seen by many film historians as one of the great tragedies of Hollywood. The Arbuckle trial was a major media event, and stories in William Randolph Hearst's newspaper empire made Arbuckle appear guilty. After two trials resulted in hung juries, the third resulted in an acquittal and a written apology from the jury—a gesture unprecedented in American justice.
Although Arbuckle was completely cleared of the allegations involving Rappe, the resulting infamy destroyed his career and his personal life. During the trial, morality groups nationwide called for Arbuckle to be sentenced to death, and studio moguls ordered Arbuckle's friends in the industry not to come to his public defense. Charlie Chaplin was out of the country at the time, on a triumphant return to England. But Buster Keaton did, however, make a public statement in support of Arbuckle, calling Roscoe one of the kindest souls he had known.
http://en.wikipedia.org/wiki/Fatty_Arbuckle