Joseph Brooks, 73, was discovered in his Upper East Side apartment around 12:30 p.m. by a friend with whom he had planned to have lunch, police spokesman Paul Browne said. It was not immediately clear how long his body had been there. The apartment door was left unlocked, police said.
Brooks' death comes five months after his son was arrested in an unrelated, high-profile case. The son was charged with murdering his fashion designer girlfriend, whose body was found in December in an overflowing bathtub at a swank hotel in SoHo.
The elder Brooks was discovered slumped over on a couch in the den, fully-clothed, with a plastic dry-cleaning bag around his head and a towel wrapped around his neck, Browne said. A hose attached to a helium tank was hooked up to the bag, he said.
According to police, Brooks told the doorman at his apartment that a friend was meeting him for lunch and had permission to enter the building. Police believe Brooks left the apartment unlocked so his friend could find him.
The medical examiner will perform an autopsy to determine the cause of death. Police said a rambling, three-page suicide note was found that included complaints about his health. They did not elaborate.
Brooks suffered a stroke in 2008, and his lawyer had said the songwriter's health was deteriorating during the court case. He appeared gaunt and shuffled slowly as he came to recent court dates.
Helium is difficult to detect in an autopsy. Using it to commit suicide is outlined in a best-selling suicide manual by British author Derek Humphry.
Brooks was awaiting trial on allegations that he molested women who were lured to his apartment for supposed acting auditions. He pleaded not guilty.
Brooks' lawyer and Manhattan prosecutors had no immediate comment about Brooks' death.
Brooks won the Academy Award for best original song for the 1977 Debby Boone ballad "You Light Up My Life" and directed a movie of the same name. It is about a comedian who has a one-night stand with a director. Brooks also won a Grammy for the song.
He pleaded not guilty in 2009 to rape, sexual abuse and other charges in the attacks on 13 women. His trial date had not been set.
Prosecutors say he lured most of the women to his apartment through an online ad offering auditions for a movie role, then sexually assaulted them after making them drink apparently drugged wine as part of an "acting exercise."
Brooks' son, Nicholas, is charged with murder in the death of his girlfriend, Peruvian-American swimsuit designer Sylvie Cachay.
She was found dead, half-clothed and face-up, in a tub at the Soho House, an elite club and hotel, after water began leaking through to the floor below. The 24-year-old had little contact with his father in recent years, authorities have said.
Nicholas Brooks has pleaded not guilty and is being held without bail at the Rikers Island jail complex.
Associated Press writer Jennifer Peltz contributed to this report.