NEW YORK (AP) — A man standing with his wife on a Bronx subway platform was pushed onto the tracks Sunday morning by another man and was struck and killed by an oncoming train, police said. The assailant fled.

Police said an unidentified man pushed 61-year-old Wai Kuen Kwok of the Bronx off the platform at the Grand Concourse and East 167th Street station in the Highbridge neighbourhood, an act that appeared to be unprovoked. Kwok was struck by a southbound D train at around 8:40 am and pronounced dead at the scene; his death was classified a homicide. His wife was not injured.

There was no indication that Kwok knew the man or had had an altercation with him before he was pushed, police said. Witnesses told police they believed the man fled the subway station after shoving Kwok and jumped on a city bus.

Police later released video surveillance showing a man wearing a dark jacket getting off a city bus and walking into a store. The man emerges moments later smoking a cigarette and strolls away. Police said the man was wanted for questioning in connection with Kowk’s death.

There have been three other incidents in recent years that involved a person being pushed onto the tracks.

In April 2013, a train ran over a man desperately clawing at a Manhattan subway platform after being pushed onto the tracks by a homeless suspect with whom he’d been arguing.

In December 2012, another homeless man was arrested for pushing a Queens straphanger in front of a Times Square train that fatally crushed him.

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