Nicholas Brooks, 24, was ordered held without bail during his initial court appearance where he was charged with attempted murder and strangulation in the investigation surrounding Peruvian-American Sylvie Cachay's death.
Prosecutors said an apology letter from Brooks to Cachay was found in her purse and showed Brooks hadn't accepted that their relationship was ending.
Brooks' attorney, Jeffrey C. Hoffman, said Saturday before his court appearance that Cachay was "absolutely fine" when last seen by her boyfriend.
"There's no question in my mind that he's not guilty of any criminal charges in this case," Hoffman said.
Cachay, 33, was discovered, half-clothed and faceup, in a tub at the Soho House hotel around 3 a.m. Thursday, after water began leaking through to the floor below. She had red marks around her neck and a bite mark on her hand, investigators said.
Brooks is the son of Joseph Brooks, who won an Academy Award for best original song for the 1977 ballad "You Light Up My Life." The elder Brooks also wrote and directed the movie "You Light Up My Life" about a comedian who has a one-night stand with a director.
Police say Cachay's death has been ruled a homicide, and the medical examiner's office is awaiting toxicology test results to determine the cause. The results aren't expected until next week.
According to court papers, an autopsy performed Thursday showed that Cachay's injuries "were not self-inflicted or accidentally caused."
Before Cachay's body was found, Brooks was seen leaving the hotel, then returning and leaving again. According to police, he told investigators he ran into a friend in the lobby, and the two left to get drinks. He returned around 3:30 a.m. to find police at the hotel.
Besides a hotel employee who delivered ice to Cachay's room, no one else was seen entering between 12:30 a.m. and 2:49 a.m., when her body was discovered, court papers said. Brooks left the hotel about 2:15 a.m., saying he was heading to a bar.
A bottle of prescription pills was discovered in the room, but no illegal drugs were found.
Brooks was at a police station for more than a day and cooperated with investigators, police said. Hoffman said Brooks was at the police precinct "without sleep for many, many hours and questioned for a long period of time."
Nicholas Brooks' father is also fighting criminal charges in an unrelated case. Joseph Brooks, 72, has pleaded not guilty to rape and other charges after being accused of sexually assaulting 11 women who came to his Manhattan apartment to audition for supposed movie roles.
Cachay lived in an apartment in Manhattan's West Village and had a membership at the Soho House, an elite club and hotel that has hosted such stars as Nicole Kidman and Naomi Watts.
Earlier in the week, a candle sparked a small bedroom fire at Cachay's apartment, and that may have led her to stay at the Soho House, police said.
Cachay and Brooks had been dating for about six months, according to her mother, Sylvia Cachay of McLean, Virginia. But she said her daughter had told her two weeks ago that the relationship was over.
The daughter, who grew up in both the U.S. and Peru, worked for Victoria's Secret before leaving in 2006 to start a swimsuit collection. She had recently been working at fashion houses again after the economy soured and she lost her backing.