By Ellen Barry and Mansi Choksi

MUMBAI, India — At 5:30 p.m. on that Thursday, four young men were playing cards, as usual, when Mohammed Kasim Sheikh’s cellphone rang and he announced that it was time to go hunting. Prey had been spotted, he told a friend. When the host asked what they were going to hunt, he said, “A beautiful deer.”

As two men rushed out, the host smirked, figuring they did not like losing at cards.

Two hours later, a 22-year-old photojournalist limped out of a ruined building. She had been raped repeatedly by five men, asked by one to re-enact pornographic acts displayed on a cellphone. After she left, the men dispersed to their wives or mothers, if they had them; it was dinnertime. None of their previous victims had gone to the police. Why should this one?

The trial in the Mumbai gang-rape case has opened to a drowsy and ill-attended courtroom, without the crush of reporters who documented every twist in a similar case in New Delhi in which a woman died after being gang-raped on a private bus. The accused, barefoot, sit on a bench at the back of the courtroom, observing the arguments with blank expressions, as if they were being conducted in Mandarin. All have pleaded not guilty. They are slight men with ordinary faces, nothing imposing, the kind one might see at any bus stop or tea stall.

But the Mumbai case provides an unusual glimpse into a group of bored young men who had committed the same crime often enough to develop a routine. The police say the men had committed at least five rapes in the same spot. Their casual confidence reinforces the notion that rape has been a largely invisible crime here, where convictions are infrequent and victims silently go away. Not until their arrest, at a moment when sexual violence has grabbed headlines and risen to the top of the state’s agenda, did the seriousness of the crime sink in.

An editor at the photographer’s publication, who was present when a witness identified the first of the five suspects, a juvenile, said the teenager dissolved in tears as soon as he was accused.

“It was exactly like watching a kid in school who has been caught doing something,” said the editor, who spoke on the condition of anonymity to protect the identity of the victim, who cannot be identified according to Indian law. “It’s like a bunch of kids who found a dog and tied a bunch of firecrackers to its tail, just to see what would happen. Only in this case it was far more egregious. It was malevolent, what happened.”

In spots Mumbai is an anarchic jumble, its high-rise buildings flanked by vest-pocket slums and vacant properties that have reverted to near-wilderness. One such place is the Shakti Mills, a ruin from the prosperous days of Mumbai’s textile industry. When night falls, it is a treacherous span of darkness lined with sinkholes and debris, but still in the middle of the city, still close enough to look up and watch the lights flicker on in the Shangri-La Hotel.

The photographer and her colleague, a 21-year-old man, were interns at an English-language publication and had decided to include this spot — the backdrop for any number of fashion shoots — as part of a photo essay on the city’s abandoned buildings, the editor said. On that Thursday last August, they reached the ruined mill about an hour before sunset.

The five men they encountered there later came from slums near the mill complex, claustrophobic concrete warrens where electrical wires tangle at one’s head and acrid water flows in open gutters around one’s feet.

None of the men worked regularly. There were jobs chicken-plucking at a neighborhood stand — a hot, stinking eight-hour shift that paid 250 rupees, or $4. The men told their families they wanted something better, something indoors, but that thing never seemed to come. They passed time playing cards and drinking. Luxury was pressed in their faces in the sinuous form of the Lodha Bellissimo, a 48-story apartment building rising from an adjacent lot.

“Every boy in this neighborhood, including myself, would look at those buildings and say, ‘One day, I will own a flat in that building,’ ” said Yasin Sheikh, 22, who knew two of the accused men from the neighborhood. Because of his work helping find slum locations for film crews, he sometimes has a chance to interact with wealthy people, he said, and it fills him with yearning.

“I feel really sad around them, because I want to sit at the table with them,” he said.

Only Kasim Sheikh, 20, the card player who took the call, seemed to have shaken off the drag of poverty. A plump man in a neighborhood of the half-starved, he wore flashy shirts and hooked up his friends with catering jobs at weddings. He had been convicted of theft — iron, steel and other scrap from a railroad site — and occasionally provided information to the police, according to Mumbai’s joint police commissioner, Himanshu Roy.

Some people steered clear of Mr. Sheikh. The grandmother of one of the accused men, a 16-year-old whose name is being withheld because of his age, had forbidden Mr. Sheikh to cross their threshold. But her grandson craved nice things; that was his weakness, his grandmother said. Mr. Sheikh “wore good clothes, he had a nice mobile, obviously he would, because he was a thief,” said Yasin Sheikh, the neighbor.

When another of their friends, a 27-year-old father of two named Salim Ansari, spotted the interns in the mill that day, the first thing he did was call Kasim Sheikh to tell him that their prey had arrived.

Nothing to Lose

During the year since the Delhi gang rape, sexual violence has been discussed endlessly in India, but there are few clear answers to the questions of how much is it happening or why.

One problem is that perpetrators may not view their actions as a grave crime, but something closer to mischief. A survey of more than 10,000 men carried out in six Asian countries — India not among them — and published in The Lancet Global Health journal in September came up with startling data. It found that, when the word “rape” was not used as part of a questionnaire, more than one in 10 men in the region admitted to forcing sex on a woman who was not their partner.

Asked why, 73 percent said the reason was “entitlement.” Fifty-nine percent said their motivation was “entertainment seeking,” agreeing with the statements “I wanted to have fun” or “I was bored.” Flavia Agnes, a Mumbai women’s rights lawyer who has been working on rape cases since the 1970s, said the findings rang true to her experience.

“It’s just frivolous; they just do it casually,” she said. “There is so much abject poverty. They just want to have a little fun on the side. That’s it. See, they have nothing to lose.”

The photographer and her colleague reached the mill but, visually, it was not what they wanted. That is when two men approached them, the victim told the police later, offering to show them a route farther in. There the images were better, and the two had been working for half an hour when the two men returned.

‘The Prey Is Here’

This time they came back with a third, Mr. Sheikh, who told them something odd — “Our boss has seen you, and you have to come with us now” — and insisted they take a path deeper into the complex. As they walked, she called an editor, who said to leave immediately, but it was too late for that. “Come inside, the prey is here,” Mr. Sheikh called out, and two more men joined them.

The men said that the woman’s colleague was a murder suspect, asked the pair to remove their belts and used them to tie the man up. After that, the woman told the police, “the third person and a person who had a mustache took me to a place that was like a broken room.”

The men had done the same thing a month before, said Mr. Roy, the police commissioner, taking turns raping an 18-year-old call-center worker who, accompanied by her boyfriend, had sprained her ankle and was trying to take a shortcut through the mill. They had done the same thing with a woman who worked as a scavenger in a garbage dump, and a sex worker, and a transvestite, Mr. Roy said.

Mr. Sheikh took the broken neck of a beer bottle out of his shirt pocket and thrust it at the young woman, telling her: “You don’t know what a bastard I am. You’re not the first girl I’ve raped,” she told the police later, according to the charge sheet filed in the case.

On the other side of the wall, her friend heard the woman cry out. “An inquiry is going on,” the man guarding him said. They went in to her and returned, one by one.

“Did you inquire properly?” Mr. Sheikh said to one as he came out.

“No, she’s not talking,” he replied.

So Mr. Sheikh said he would “go inquire again,” and the rest of them laughed.

At last they brought her out, weeping, and told the two to leave along the railroad tracks. Before releasing her, they threatened to upload video of the attack onto the Internet if she reported the crime, a strategy that had worked with previous victims.

But this one did not hesitate. The two caught a cab to the nearest hospital. There they reported the crime, and the woman’s mother arrived. “I went inside. I saw her there crying,” her mother told the police later. “She told me in English, ‘Mummy, I’m vanished.’ ”

The woman did not respond to a request for an interview.

Mr. Sheikh, too, saw his mother for a few moments that night. He discussed the rape with her, she said, and tried to explain why it had happened.

“I asked Kasim, ‘Son, why did you do this to her? If it happened to your sister, would you come here and tell me or would you beat him?’ ” said his mother, Chandbibi Sheikh. He told her that his friends had come upon the couple embracing in the mill, and “they thought: ‘What is she doing with this boy here? She must be loose.’ ”

She related this exchange from the family’s home, a sort of shelf wedged between a gas station and a garbage dump; as she spoke, a rat the size of a kitten clambered over containers stacked in a corner. She said far too much onus was being put on the men.

“Obviously, the fault is the girl’s,” she said. “Why did she have to go to that jungle? It’s her fault, too. Also, she was wearing skimpy clothes.”

She did not deny that he had done it. “He must have,” she said. “He told me that they tied up the boy who was doing bad things to her and said, ‘Madam, let us also do it.’ The madam said, ‘Don’t do it to me, take my mobile, take my camera, but don’t do it to me.’ Her body was uncovered. How could he control himself? And so it happened.”

High-Level Response

Though the men in the mill may not have known it, rape had become a matter of great public import in India, a gauge of a city’s identity. Mumbai’s top officials, who had told themselves that the Delhi gang rape could not have happened here, were horrified and initiated a broad, high-level response, as if an act of terrorism had taken place.

The police lighted up their networks of slum informants and all five were arrested and gave confessions in quick succession. Several made pitiful attempts to escape. Mr. Sheikh went to the visitor’s room of a nearby hospital and covered himself with a blanket, trying to blend in with a crowd of relatives. He was caught with 50 rupees, or about 81 cents, in his pocket. When the police asked him to sign his confession, he told them he could not write, so he signed it with a thumbprint.

“It is incredible how quickly the whole thing unraveled,” said the editor, who was present when the photographer’s colleague picked the first of the five men out of a lineup. A second victim, the call-center worker, came forward, inspired by the first, and said she was ready to testify. The suspects confessed to the other rapes under questioning, the police said.

The public prosecutor selected for the case is famous for prosecuting terrorists, with a résumé of 628 life sentences, 30 death sentences and 12 men, as he put it, “sent to the gallows.”

Much news coverage over the next days zeroed in on the defendants’ poverty, but Mr. Roy shrugged off that line of inquiry. After interrogating the five accused men personally, he said they were “social outcasts,” not indicative of any deeper tensions in the city.

“They were deviants, sociopaths, predators,” he said in an interview. “If there was a larger socioeconomic framework, these crimes would be happening again and again. It was only these guys. I’m 100 percent sure that this kind of crime doesn’t happen in Mumbai. I’ve been here all my life and have been born and brought up here.”

But in a constellation of neighborhoods around Mumbai, people are still trying to match up the crime with the ordinary men they knew.

Shahjahan Ansari, the wife of the oldest accused man, Salim Ansari, looked terrified when a stranger appeared at her door, at a hulking, trash-strewn public housing complex beside a petroleum refinery on a distant edge of the city. The neighbors had started to shun the family since Salim’s arrest became public, and she dreaded the extra attention.

“We can’t even walk on the street. You don’t understand,” she said. Inside the apartment, she calmed down a little. The whole story baffled her; she said she had no idea who her husband’s friends were or what he did during the day when she went to work cleaning houses. All she knew was that until his arrest, he came home for dinner every night, “He was to me like any husband is to his wife,” she said.

“How do I know how he got into this mess? It must be the Devil,” murmured Salim’s mother, who was sitting on the floor, one eye blind, cloudy white.

Ms. Ansari was remembering better days before her husband lost his job, at a factory that made cardboard boxes. He was so proud of the factory, with its big machines, that he brought his sons to watch him on Sunday shifts. Tonight the younger one was streaked with dust; the older one watched from a cot, glassy-eyed and much smaller than his 10 years, bony limbs folded under his chin. She would try, Ms. Ansari said, to move them somewhere else, to a place where no one knew who their father was.

“I want my children to grow up to be good human beings, that’s all,” the mother said.

Neha Thirani Bagri contributed reporting.

A version of this article appears in print on Oct. 27, 2013, on Page A1 of the New York edition with the headline: Gang Rape, Routine and Invisible. Lead photo by Atul Loke; photo of Chandbibi Shaikh by Sami Siva.