The 30-year-old Queens man was picked up by police at 50th Street and 7th Avenue at around 2 p.m. this afternoon.
Police say he was spotted on surveillance video working with street vendors. Detectives kept an eye on that corner, where numerous street vendors traditionally work.
During interviews with street vendors, detectives also learned he had worked at a nearby deli.
According to police sources, they talked to the deli manager, who recognized him and identified the man's voice in the video.
Police identified the victim as 58-year-old Ki-Suck Han, of Queens.
Video shows the suspect police are searching for, and authorities are hoping the video and other pictures will lead to an arrest.
Witnesses say it was a terrifying attack that happened around 12:30 in the afternoon at the 49th Street station that serves the Q, N and R lines.
An argument between Han and the suspect escalated and ended with Han being thrown onto the tracks. As he desperately struggled to climb out of the track-bed, an oncoming train pinned him against the platform.
The suspect fled the scene, running north along Seventh Avenue.
"I just heard people yelling," witness Patrick Gomez said. "The train came to an abrupt stop three-quarters into the station, and that's when I heard that a man was hit by a train."
Police say the suspect is 5-foot-10 to 6-feet tall and weighs about 200 pounds. He is in his 20s, has short dreadlocks and was last seen wearing a gray T-shirt and a black jacket.
Authorities say he may be emotionally disturbed and he could still be in the area of the station.
Police have been scanning the crowds and mapping surveillance cameras, trying to learn where the fleeing man was headed in the minutes after the killing.
Han leaves behind a wife and daughter. His wife says the couple had a fight about 90 minutes before the incident. She also said her husband may have been drinking at the time.
Several subway riders who witnessed the death were treated for trauma.
Anyone with information in regards to this case is asked to call Crime Stoppers at 1-800-577-TIPS (8477).
Information from WABC-TV in New York