The victim, Sunando Sen, was from India, but it isn’t clear whether he was Muslim or Hindu, it doesn’t matter.

The arrest capped a three-day search for a heavyset, 5-foot-5 Hispanic woman who was caught on camera escaping from a subway platform in Sunnyside, Queens, after she allegedly shoved a man into the path of an oncoming No. 7 train. It was the second such attack in New York City in less than a month.

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

“When a murder happens in New York, it can often be dismissed as being in someone else’s backyard,” said Gene Russianoff, staff lawyer for the Straphangers Campaign, a rider advocacy group. “The subway is everyone’s backyard.”

The police identified the victim as Sen of Queens, a 46-year-old immigrant who had been raised in India and who, after years of toil, had finally saved enough money to open a small copying business this year on the Upper West Side of Manhattan.

Ar Suman, one of four roommates who shared a small first-floor apartment with Sen in Elmhurst, 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 the business, New Amsterdam Copy.

Since the shop opened, he had rarely taken a day off, Suman said.

“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.”‘

Police Commissioner Raymond W. Kelly said Friday that according to witnesses’ accounts, there was no contact on the platform between the attacker and the victim immediately before the fatal shove. He said Sen was looking out over the tracks when his attacker approached him.

The attack occurred so quickly, with the train already barreling into the station, that the man had little time to react and bystanders had no time to try to help, said Paul J. Browne, the Police Department’s chief spokesman.

Sen was hit by the first car and his body was pinned under the second car 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 and running along Queens Boulevard. She was described by the police as Hispanic, 5 feet 5 inches tall, in her early 20s and heavyset. She was reported to be wearing a blue, white and gray ski jacket and Nike sneakers — gray on top, red on bottom.

The subway station was closed overnight as officers from the Emergency Services Unit used specialized inflatable bags to lift the train and recover the victim’s remains. The No. 7 line had resumed normal service by the morning rush.

Sen’s roommates could not understand what might have led to the fatal encounter Thursday.

Suman said that as far as he knew, Sen did little more than work and come home. Both his parents were dead, they said, and he was not married and had no children.

Sen suffered a heart attack about nine months ago, Suman said, but did not slow down. The night stand 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.”