A 58-year-old subway passenger was killed on Monday after he was pushed onto the tracks of an onrushing train in Manhattan by a man who had been mumbling to himself as he walked along the platform, the police said.

The passenger, identified by the police as Ki-Suck Han of 52nd Avenue in Queens, tried to climb back onto the platform but did not make it; he was struck by a southbound Q train in the 49th Street station. He was pronounced dead at St. Luke’s-Roosevelt Hospital, the police said.

The assailant fled and remained at large on Monday night, the police said. Paul J. Browne, the Police Department’s chief spokesman, described the attacker as a black man in his mid-20s in a tan shirt and black pants who was carrying a black jacket and wearing a woolen hat.

On Monday night, two police officials and a priest were seen escorting a woman believed to be the victim’s wife from a Queens apartment to a van. They made no comment to reporters outside.

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The police released a brief video recorded by a woman on the platform, in which the attacker is seen and heard cursing at the victim and telling him to stand in line and wait for the train.

Some details of what happened at the subway station remained unclear.

But the episode had echoes of the kind of urban nightmare that has terrified the city before, perhaps most notoriously in 1999, when a young writer and photographer, Kendra Webdale, was pushed to her death in front of an N train at the 23rd Street station.

The police arrested a schizophrenic man who pleaded guilty to manslaughter in 2006 during his third trial.

The public furor over the attack on Ms. Webdale prompted lawmakers in Albany to enact a state statute known as Kendra’s Law, which gave judges more power to compel mentally ill people to comply with court-ordered psychiatric treatment.

The last time someone was pushed in front of a train and struck was apparently in August 2010, when a 39-year-old woman was pushed in front of an R train at 28th Street. The woman, who suffered broken bones and a punctured lung, survived.

In June of this year, a woman was pushed to the tracks by a stranger in the Bronx but was pulled to safety.

The episode on Monday unfolded about 12:30 p.m. beneath the fluorescent lights of the station, which opens onto Seventh Avenue. One entrance is just steps from Father Duffy Square, a few steps north of Times Square, where tourists and theatergoers line up at a booth that sells discount tickets to Broadway shows.

Several bystanders were treated at the scene, apparently for shock or trauma, fire officials said.

Mr. Browne said that moments before the episode, witnesses saw a man who was “talking to himself.”

“He gets into an argument and is pushing and shoving,” Mr. Browne said, “and at least one witness felt that the aggressor was emotionally disturbed.”

The man approached the victim, and “the two exchanged words,” Mr. Browne said.

The man pushed the victim onto the tracks. “As he attempted to climb out of the well, he was struck by the train and got wedged between the platform and the train car,” Mr. Browne said.

Witnesses said the train screeched, apparently as the train operator hit the brakes. But it traveled about 80 percent of the length of the first car, or nearly 50 feet, before it finally stopped, Mr. Browne said.

Investigators said they believed that the two men did not know each other and that the suspect may have “picked a fight,” Mr. Browne said.

One subway rider, Patrick Gomez, said he had just swiped his MetroCard to enter the station when he heard yelling on the platform. He said he heard a “thud that didn’t sound normal” as the train pulled in.

Reporting was contributed by Cara Buckley, Randy Leonard, Andy Newman, William K. Rashbaum, Wendy Ruderman, and Michael Schwirtz.