NEW YORK - Police sought answers Wednesday from a retired corrections officer after his dispute with two strangers ended with a fatal shooting that spread panic in a subway station at the height of the evening rush.

The former officer, whose name was not made public, shot Gilbert Drogheo at about 6:30 p.m. Tuesday at the Borough Hall station in Brooklyn, police said. Investigators took him into custody but released him without charges after he agreed to meet Wednesday for more questioning.

The mayhem began when the 69-year-old retired officer boarded a Brooklyn-bound subway train in Manhattan, police said. He had a small Ruger handgun that he was licensed to carry in public, they said.

According to witnesses, it appeared that the former officer angered Drogheo, 32, and a younger man by stepping in between them as they talked, police said. The men and the officer argued before they pushed him into an empty seat on the train, police said.

All three men exited the train at the next stop in Brooklyn, where there was a second confrontation, police said. The retired officer tussled with Drogheo before pulling his weapon and firing one round that hit the victim in the chest, they said.

New York Police Department officers assigned to the station heard the shot and detained the suspected shooter. Drogheo died at the hospital. His companion was taken into custody.

WCBS broadcast a cellphone video showing a man - identified by the TV station as the retired officer - cornering a smaller man near an exit in the Brooklyn subway station and pushing him. The men are seen struggling before a gunshot is heard and bystanders scatter.

Thomas Berry, a subway passenger who said he witnessed the dispute, told the Daily News that the older man had initially tried to avoid trouble.

The officer told the men, " 'Leave me alone, don't talk to me,' " Berry said. "He was being really calm."

But as the dispute grew more heated, the older man flashed a gun, Berry said.

"Everyone said 'Gun!' and ran off the train," he said.