According to the paper, the dispute began at around 6:30 p.m. when the victim and an associate began harassing the 69-year-old gunman as he boarded a Brooklyn-bound 5 train. From the Daily News:
The witness said one of the assailants told the older man "Oh, I got you now my 'N——,'" as the retired officer tried to walk between the younger men to get on the train.
"(The older man) said 'I'm not your n——, I'm not your boy," the witness said.
Things got heated as the train went under the East River, then turned violent when one of the younger men punched the older man in the head as he tried to get off at Borough Hall, the witness said.
"He just clocked the guy," the witness said. "The older man was taken back, I saw him pull the gun out of the pocket."
The Daily News' witness says the older man then put a clip in his gun and cornered the younger man, who had fled onto the platform. CBS News claims to have obtained a video showing what happened next:
In the video, the gunman is seeing walking through the station as witnesses yell out to him, "Don't shoot!" But then, he walks up to a man in a black shirt and camouflage pants and shoves him.
They wrestle, and the gun goes off.
Police say the victim was then taken to a Brooklyn hospital, where he died.
[There was a video here]
UPDATE - 11:20 a.m.: Citing law enforcement sources, The New York Times has identified the victim as 32-year-old Gilbert Drogheo and the gunman as 69-year-old Wiliam Groomes. According to the Times, police took Groomes to a nearby hospital for treatment and Drogheo's 29-year-old associate to a police station for questioning. As of Wednesday morning, no charges have been filed.