Investigators recovered security video showing a man fitting the description of the suspect working with street vendors near Rockefeller Center, said New York Police Department spokesman Paul Browne.
"The individual we talked to made statements implicating himself in the incident," Browne said.
Witnesses told investigators they saw the suspect talking to himself Monday afternoon before he approached Ki-Suck Han at the Times Square station, got into an altercation with him and pushed him into the train's path.
Police took the man into custody Tuesday, but no charges are expected to be announced until Wednesday, Browne said.
Han, 58, of Queens, died shortly after being struck. Police said he tried to climb a few feet to safety but got trapped between the train and the platform's edge.
The Post published a photo on its front page Tuesday of Han with his head turned toward the train, his arms reaching up but unable to climb off the tracks in time. It was shot by freelance photographer R. Umar Abbasi, who was waiting to catch a train as the situation unfolded.
Abbasi said in an audio clip on the Post's website that he used the flash on his camera to try to warn the train driver that someone was on the tracks. He said he wasn't strong enough to lift Han.
"I wanted to help the man, but I couldn't figure out how to help," Abbasi said. "It all happened so fast."
Emotional questions arose Tuesday over the published photograph of the helpless man standing before the oncoming train accompanied by the headline that read in part: "This man is about to die."
The moral issue among professional photojournalists in such situations is "to document or to assist," said Kenny Irby, an expert in the ethics of visual journalism at the Poynter Institute, a Florida-based nonprofit journalism school.
Other media outlets chimed in on the controversy, many questioning why the photograph had been taken and published.
"I'm sorry. Somebody's on the tracks. That's not going to help," said Al Roker on NBC's "Today" show as the photo was displayed.
CNN's Soledad O'Brien tweeted: "I think it's terribly disturbing -- imagine if that were your father or brother." Larry King reached out to followers on Twitter to ask: "Did the (at)nypost go too far?"
The Post declined to share the photo with The Associated Press for distribution.
Subway pushes are feared but fairly unusual. Among the more high-profile cases was the January 1999 death of Kendra Webdale, who was shoved to her death by a former mental patient.
After that, the Legislature passed Kendra's Law, which lets mental health authorities supervise patients who live outside institutions to make sure they are taking their medications and aren't a threat to safety.
Mayor Michael Bloomberg said Tuesday that he believed that "in this case, it appeared to be a psychiatric problem."
The mayor said Han, "if I understand it, tried to break up a fight or something and paid for it with his life."
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