Signs pointed to a suicide or an accidental overdose, police sources said.

28-year-old Ledger was found naked and unconscious on a bed, with sleeping pills — both prescription medication and nonprescription — on a night table. The security attempted to revive him, but he did not respond.

Ellen Borakove, a spokeswoman for the office of the city’s chief medical examiner, Dr. Charles S. Hirsch, said that employees of the office were at the apartment and that an autopsy would be conducted on Wednesday.

Paul J. Browne, the Police Department’s deputy commissioner for public information, initially said that the apartment was owned by the actress Mary-Kate Olsen, but later reversed himself and said that was not the case.

A representative of Ms. Olsen said that the apartment did not belong to the actress. “It is not her apartment,” the representative, Annette Wolf, a publicist for Ms. Olsen, said in a phone interview. “She does not own the apartment. She has never owned the apartment. She and her sister have an apartment in New York City but they are not in this building.”

Heath Ledger was nominated for an Oscar for Best Actor in January 2006 for his role in "Brokeback Mountain". While filming the movie, he met the actress Michelle Williams and they had a daughter, Matilda Rose, who was born on Oct. 28, 2005. The couple separated last year.

In an interview in London for an article published in November, Heath Ledger told The New York Times, "I feel like I’m wasting time if I repeat myself."

Heath Ledger had been cast as The Joker in the latest Batman installment, “The Dark Knight,” set to be released this summer.