NEW YORK — 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.