Commuters wait on the platform on Friday as a train passes through the station in Queens, New York, where Sunando Sen was killed. (AP)

New York, Dec. 29: Like so many busy New Yorkers in a hurry to get where they have to go, former Calcuttan Sunando Sen peered out over the tracks on an elevated subway stop in Queens on Thursday evening, anxiously awaiting the next train.

What he did not see, the authorities said, was a woman approaching from behind who had been sitting on a bench and had been heard mumbling to herself.

Before Sen could react, the woman pushed him into the path of a No. 7 train roaring into the 40th Street-Lowery Street subway station in Sunnyside. Sen was crushed under the train.

As onlookers screamed, the woman fled the station down two flights of stairs. Her image was captured by a security camera as she ran down Queens Boulevard, casting a wary glance over her shoulder. She remains at large.

Sunando Sen

Sen, a 46-year-old Queens resident, hailed from Calcutta and co-owned New Amsterdam Copy, a printing shop on Amsterdam Avenue, The New York Post reported.

“He studied at Delhi University. He got a scholarship to NYU, where he graduated. He almost finished his PhD, but he didn’t,” the newspaper quoted his business partner Sanjeeb Das as saying.

Sen had, after years of toil, finally saved enough money to open his small copying business this year. Both his parents were dead and he was not married and had no children, said his four roommates who shared a small first-floor apartment with Sen in Elmhurst.

A.R. Suman, one of Sen’s roommates, said he was driving a client upstate when another roommate called and told him what had happened. Hoping the information was wrong, Suman raced back to the city, only to find that there was nothing he could do — Sen was dead.

“He was a very educated person and quite nice,” Suman said. “It is unbelievable. He never had a problem with anyone.”

Suman said Sen was proud when he had saved enough money to open his business. Since the shop opened, he had rarely taken a day off.

“I asked him why do you work seven days a week?” Suman said. “He told me, ‘I cannot hire someone because business is not good’.”

Sen’s roommates could not understand what might have led to the attack. Suman said that as far as he knew, Sen did little more than work and come home. Sen suffered a heart attack about nine months ago, Suman said, but did not slow down.

The nightstand in Sen’s bedroom had many bottles of prescription medicine. Across the room on his desk was a pile of medical bills.

His roommates said he liked watching funny clips on YouTube to unwind, enjoyed a cup of tea and would relax listening to classical Indian music.

“This guy is so quiet, so gentle, so nice,” said M.D. Khan, a taxi driver who also lives in the apartment. “It’s so broken, my heart.”

Police commissioner Raymond W. Kelly said that according to witnesses, there was no contact on the platform between the attacker and the victim immediately before the fatal shove.

The attack occurred so quickly, with the train already barrelling into the station, that the victim had little time to react and bystanders had no time to try to help, the police said.

Sen was hit by the first car and his body was pinned under the second before the 11-car train came to a stop.

Investigators released a grainy black-and-white video overnight showing a person they identified as the attacker fleeing the station.

She was described by the police as Hispanic, five-foot-five, in her early 20s and heavyset. She was reported to be wearing a blue, white and gray ski jacket and Nike sneakers — grey on top, red on bottom.

The seemingly unprovoked attack, the second time this month that a man was thrown to his death on the subway tracks, stirred some of New Yorkers’ deepest fears.

For the millions who travel on the city’s subway trains every day, the thought of being thrown onto the tracks is a fleeting fear at most. But each time there is an attack, people tend to stand a little farther from the tracks, at least for a while.

Mayor Michael R. Bloomberg said such attacks were exceedingly rare, but that statistics did not diminish the tragedy for the families of the victims.

“You can say it’s only two out of the three or four million people who ride the subway every day, but two is two too many,” he said.

“I don’t know that there is a way to prevent things. There is always going to be somebody, a deranged person.”

He added: “We do live in a world where our subway platforms are open, and that’s not going to change.”

In 1999, two attacks in which mentally ill people pushed unsuspecting victims into the path of oncoming subway trains, one fatally, led to legislation giving families the right to demand court-ordered outpatient psychiatric treatment for their relatives.

Known as Kendra’s Law, it permits state judges to order closely monitored outpatient treatment for seriously mentally ill people who have records of failing to take medication, and who have frequently been hospitalised or jailed or have exhibited violent behaviour.