According to a person familiar with the investigation, that determination was made by the responding supervisor on the midnight shift who told patrol officers that the man, Mr. Rispoli, had been the victim not of an assault, but of a drunken fall. It was not clear, the person said, what led the supervisor to that conclusion, or how the victim’s wounds appeared to officers.

A police summary of the crime days later said that officers had found Mr. Rispoli unconscious; more recently, the police said he had been awake and vomiting, but unable to communicate.

A witness, who called 911 and remained at the scene, said officers there never questioned him. “They didn’t talk to nobody that night,” said the witness, a 55-year-old Sunnyside resident who requested anonymity because the killers remained at large.

About two hours before the attack, Mr. Rispoli left the apartment on 51st Street that he shared with his husband, Danyal Lawson, for one of his routine, late-night meanderings. He did not bring a wallet or his cellphone, though he may have had some pocket cash, Mr. Lawson said.

“Lou used to go out walking all the time, until two or three in the morning,” he said. “It’s just something he did from a young age to get some peace from his crazy Italian family.”

Mr. Rispoli — known by friends as the Lion for his 6-foot-2-inch frame and shaggy mop of brown hair — would strike up conversations as he wandered, never along a set route. “He was a New Yorker,” Mr. Lawson said. “He never felt unsafe.”

Whom he encountered on his walk that night remains a mystery. But shortly after 2 a.m., the witness saw Mr. Rispoli exiting a white two-door sports car with three men. As one of the men stood watch from the corner of 42nd Street, Mr. Rispoli walked between the other two along 43rd Avenue, according to the witness, who called 911.