NEW YORK (AP) — Police on Monday hunted for the man who shoved a stranger off a subway platform to his death and released surveillance footage of the suspect walking calmly away from the station just minutes after the fatal push.

Wai Kuen Kwok, 61, was standing with his wife on the platform at the Grand Concourse and East 167th Street station in the Highbridge neighborhood of the Bronx Sunday when he was pushed from behind. Kwok was struck by a southbound D train at around 8:40 a.m. and pronounced dead at the scene. His wife was not injured.

There was no indication that Kwok knew the man or had had any interaction with him before he was pushed, police said. His wife said she did not recognize the man. The suspect fled the station and hopped on a city bus, police said.

Surveillance footage shows the suspect walking calmly from the subway station. Later footage shows him getting off a bus, heading into a convenience store and then emerging smoking a cigarette. The man is balding and was dressed in a leather jacket, dark pants and white sneakers. Police are trying to determine his whereabouts.

The victim's wife, 59, was taken to a hospital for observation. Relatives told authorities Kwok worked for a kitchen supply company, and the couple was planning to have breakfast and do grocery shopping in Chinatown on Sunday.

The victim's son, Gary Kwok, a 29-year-old doctoral student at Adelphi University, told The New York Times that his father was a "fine, regular family man."

Neighbors described the family as close-knit and giving. "Whenever they go out they are always together and they always come back together," neighbor Dely Ramos, 64, told the Times.

There were at least two other cases in recent years that involved a person being fatally pushed onto the tracks.

In December 2012, a homeless man was arrested for pushing a Queens straphanger in front of a Times Square train that fatally crushed him. A photographer who happened to be on the platform snapped a series of photos of the man as he was being struck, prompting criticism that the photographer should have tried hard to help the victim.

Later the same month, a mumbling woman pushed a man to his death in front of a subway train in Queens.

About 5 million people ride the subway every day in New York City. Every year, about 140 people are hit by city subways, many of them in accidental knocks and willful leaps. Fifty people have been killed by subway trains so far this year, and 55 died last year, according to the MTA.