A retired New York City correction officer told two men he was fighting with in a Brooklyn subway station that he was a cop and would arrest them, then fired at one of the men, killing him at the height of Tuesday's evening rush, a law enforcement source tells NBC 4 New York.

The officer, identified by the source as 68-year-old William Groomes, returned to Brooklyn police precinct Wednesday for questioning after the shooting death of 32-year-old Gilbert Drogheo. Groomes, along with Joschelyn Evering, who was traveling with Drogheo at the time of the shooting, was questioned following the fray at the Borough Hall subway station and released.

Evering, 28, of Brooklyn, was arrested Wednesday and charged with assault and menacing. Bail was set at $1,500. His mother declined NBC 4 New York's request for comment.

Groomes could face an indictment if the district attorney decides to convene a grand jury.

According to a source, Groomes, Drogheo and Evering, got into an argument that turned physical after Groomes boarded a Brooklyn-bound No. 4 train at the Bowling Green station in Manhattan Tuesday evening. Groomes allegedly told police that the two men, who were already on the train when he got on, said something to him after he walked between them and then pushed the 68-year-old into an empty subway seat, the source said.

Groomes and the two men got off the train at the Borough Hall stop and started fighting on the platform, the source said. That’s when Groomes allegedly identified himself as an officer and told Drogheo and Evering that they would be put under arrest.

The source says that the men ran away, with Groomes following. As the men tried to walk out of an exit gate, Drogheo and Groomes began scuffling again. Then, the source says, Groomes pulled out a gun and fired one round, which fatally hit Drogheo in the abdomen.

The retired officer and Evering stayed at the scene. They were not hurt and no bystanders were injured, police said.

No charges have been filed against Groomes in connection with the shooting.

It wasn't immediately clear if Evering had an attorney.

Norman Seabrook, the president of the city Correction Officers' Benevolent Association, told NBC 4 New York Wednesday that they believe the retired officer was acting in self-defense. He said if the Brooklyn district attorney convenes a grand jury to hear evidence in the case, the union would stand behind the retired officer.