A man was shot and killed by a retired New York City correction officer inside a Brooklyn subway station at the height of the evening rush Tuesday, authorities and sources say.

Law enforcement sources said 32-year-old Gilbert Drogheo was shot in the torso by the unidentified 69-year-old retired correction officer near a stairwell inside the Borough Hall station at about 6:30 p.m.

Drogheo was taken to Brooklyn Hospital, where he died, authorities said.

The retired officer stayed on the scene after the shooting and he was not injured. No other bystanders were hurt, police say. The officer and another person who was with Drogheo are being questioned by police.

Police said a dispute that escalated into a physical confrontation led to the shooting.

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 DA convenes a grand jury to hear evidence in the case, the union would stand behind the retired officer.

Video posted to Instagram showed subway riders being ushered out of the station amid confusion.

Witness Fatima Manuel said she first thought she head a firecracker when the gunshot rang out.

"I was scared," she said.

Startled straphangers said firing a weapon in a crowded subway station is dangerous regardless of the justification.

"Obviously there's ricocheting and it's usually very crowded here," said Elizabeth Brett Schneider.

"I'm shocked, this is my local subway station," she said. "I'm here every morning, every evening, and this scares me. That's really frightening."

All subway entrances reopened by 4 a.m. Wednesday after being closed for hours Tuesday night. There were already widespread subway delays on at least a half-dozen lines Tuesday due to signal problems.

-- Ida Siegal and Katherine Creag contributed to this report