But on a mezzanine level of the station, the police said, the men encountered one another again and an argument again escalated into a physical confrontation. At one point, one of the men grabbed the retired officer from behind, the police said, and the older man pulled the gun from its holster.

At least one shot went off, the police said, striking one of the younger men in the chest. He was taken to Brooklyn Hospital Center, where he was pronounced dead. The police identified him early Wednesday morning as Gilbert Drogheo, 32.

The 69-year-old man, who was identified by a law enforcement official on Wednesday as Wiliam Groomes, was taken in police custody to Long Island College Hospital for treatment and was later released. The other younger man, who the police say is 29, was taken to a nearby police station for questioning. The police had not released his name. No charges had been filed as of Wednesday morning.

Norman Seabrook, the president of the New York City Correction Officers’ Benevolent Association, cautioned the public not to rush to a conclusion.

“I believe that we should wait until all circumstances are in before rushing to judgment,” Mr. Seabrook said.