It was a Sunday evening routine: heavy drinking, some rough, rustic food, and then out in the bus, cruising Delhi's streets looking for "fun". This particular Sunday, 16 December last year, was like many others for Ram and Mukesh Singh, two brothers living in a slum known as Ravi Das Colony. The "fun", on previous occasions, had meant a little robbery to earn money for a few bottles of cheap whisky and for the roadside prostitutes who work the badly lit roads of the ragged semi-urban, semi-rural zones around the edges of the sprawling Indian capital.

However, this Sunday evening was to end not with a "party", as one of the men later called their habitual outings, but with the gang-rape and murder of a 23-year-old woman. The incident was to prompt a global outcry and weeks of protests in India, and to reveal problems often ignored by those overseas who are perhaps too eager to embrace a heartwarming but simplistic narrative of growing prosperity in the world's biggest democracy.

If sympathy lay, naturally, with the 23-year-old physiotherapist who was the victim of the attack, fascination focused on her assailants. These were not serial sex criminals, psychopaths or brutalised men from the margins of society. Their backgrounds were, perhaps more worryingly, like those of tens of millions of Indian men.

Nor was Ravi Das Colony "the underbelly" of the Indian capital, as one local newspaper described it. A few hundred homes crammed on to a patch of land flanked by a road, a temple and a recently restored medieval tomb, it lies like an outpost of another, poorer India amid the relatively well-off suburbs to the south of the city.

Like hundreds of other settlements across the metropolis, all founded by squatting migrants, who have been drawn to Delhi for decades, its single-room homes are overcrowded and noisy, but its doorsteps are swept clean each night and, though police venture rarely into its narrow lanes, order is maintained by the knowledge that almost every act, even the most intimate, will be instantly known to the entire community.

For Ram and Mukesh Singh, 34 and 26 years old, Ravi Das Colony had been home for most of their lives. Ram earned a living as the driver of a bus that, albeit without the necessary permits, carried schoolchildren.

Ram Singh, who led the attack, according to his fellow accused. He died in police custody. The police said he killed himself; his family disputes this

Ram's brother, fired from a dozen jobs, intermittently drove a taxi.

The two had grown up on a small homestead in Karauli, a remote eastern part of the state of Rajasthan, five hours by train from the capital. They attended a local school with few facilities and an often absent teacher, playing in the fields and dried riverbeds. They came to Delhi in 1997. India was then beginning to boom after the reforms of the early 1990s injected a new capitalist energy into the sclerotic, quasi-socialist-quasi-feudal economy, and their landless labourer parents decided to try their luck in the capital.

Percentage of Indian population living in urban areas

But if life in the city was better than the brutal poverty of the village, the improvement was only marginal. After a decade, their father and mother returned to Karauli and the brothers stayed on in a one-room brick home, brutally hot in the heat of the summer, freezing in winter. Ram, a slim, dark, small man, married a woman with three children by another man. She died of cancer shortly afterwards without bearing him a child of his own. After her death, he started drinking heavily and fighting. When he drove his bus into a lorry, he damaged an arm permanently. (Ram later appeared on one of India's hugely popular reality shows, angrily accusing his former employer of refusing him compensation for his injury. The bus owner accused him of being negligent and rash.)

Though they left local girls alone, the Singh brothers were known among their neighbours for drunkenness, petty crime and occasional, unpredictable violence. The younger brother, Mukesh, was personable, if impressionable, according to teenagers in the neighbourhood. "He was fine on his own but different when he was with his brother," one said, speaking a few days after the incident that would make the pair, if only for a short time, globally infamous.

Ratio of Indian children aged under six

Ram Singh spent the afternoon of 16 December visiting relatives elsewhere in the city, returning home at about 5pm. The day before, a 17-year-old drifter who had worked with him a year previously as an assistant on his bus had come to collect a debt of 6,000 rupees (£70). The money was not ready and, with little else to do, the teenager had stayed on, sleeping on the bare floor of the small house. Also staying was another young man, 28-year-old Akshay Thakur, who eked out a living helping Ram Singh on his bus, and had no home of his own.

India and Pakistan income, GDP per capita

Both the 17-year-old, known as Raju, and Thakur had their own troubled histories. Their paths had taken them through a side of India that has less to do with the emerging economic powerhouse of international repute and more to do with a tenacious, older India riven by conflict, poverty, chaos and random violence.

The eldest of five children, Raju was born to a destitute day labourer with mental health issues and his wife in a village 150 miles east of Delhi, in the vast northern state of Uttar Pradesh which has 180 million inhabitants and socio-economic indicators often worse than those in sub-Saharan Africa. As in rural Rajasthan, where the Singh brothers came from, women in the countryside of Uttar Pradesh suffer systematic sexual harassment and often violence. Rape is common and gang rape frequent. Victims are habitually blamed for supposedly enticing their attackers. Many are forced to marry their assailants; others kill themselves rather than live with the social stigma of being "dishonoured". Police rarely register a complaint, let alone investigate.

When only 10 or 11 years old, Raju was sent from his village home for Delhi. Though for some time he intermittently sent his parents money, they had no idea where he was. According to Raju's statement to police, the country boy had found food, shelter and a meagre wage as a dishwasher and server in a cheap dhaba, or roadside foodstall, in a rough neighbourhood called Trilokpuri, on the margins of the city's sprawl across the northern bank of the stinking, if still holy, river Yamuna.

Created as a new home for slum dwellers cleared from Delhi's old city in the 1970s, Trilokpuri is another zone of transition, still halfway between the urban and the rural, where buffalo graze amid plastic bags and rubbish in the wastelands that separate new, poorly built cement blocks of flats.

Age of Indian population

After six months at a stall, sleeping below the tables and eating leftovers, Raju found work as a milkman's assistant before returning to washing dishes, this time at a dhaba serving Delhi's favourite street food of chole bhatura, spiced chickpeas. Finally he pitched up at a third establishment where the owner remembers a hardworking, slight and personable young man liked by the hundreds of customers, mainly rickshaw drivers, who each day paid 20 or 30 rupees for a bowl of beef curry with thick, rustic bread.

Delhi police inspect the bus believed to be the vehicle in which the woman was gang-raped. The suspects tried to run her over after throwing her off the bus. Photograph: Strdel/AFP

Raju earned 3,000 rupees a month but left in the summer of 2011 after Ram Singh, who was a regular at the dhaba, asked him to work as an assistant on his bus. After a few months he moved on again, taking a job as a cleaner at a bus station in the south of Delhi where he slept in empty vehicles but remained friends with the man from Ravi Das Colony. He had stopped sending money home and his parents, back in his remote native village, believed he was dead.

The fourth man sharing the food and cheap whisky in the Singh brothers' home in Ravi Das Colony that Sunday evening was Akshay Thakur, who also came from a distant village deep in a desperately poor and conservative part of India. He, too, had left his home, 80 miles from Patna, the state capital of Bihar, for Delhi, though his journey was less direct, taking him five years and a variety of poorly paid, often physically arduous jobs such as working in brick kilns and selling illegal home-brewed "country liquor" before he ended up replacing Raju, working on Ram Singh's bus.

The four men were thus all representative of a substantial element of contemporary Indian society. (The median age in India is 25, with two-thirds of the 1.2 billion population under 35.) They were semi-skilled and poorly educated, like so many other products of the country's failing education systems. They were migrants from the country to the town – four of the millions of individuals who over recent decades have converted an almost entirely rural country into an increasingly urbanised one. They were unmarried in a part of India where men outnumber women and gender imbalances are worsening. They were drinking in a city known for high levels of alcohol abuse. There was nothing very extraordinary about them. Yet within hours they would commit acts that would prompt outrage across the planet.

At about 8pm, after the "party" had been going for nearly three hours, Ram Singh was called by the owner of the bus he drove for a living, and asked to buy a cylinder of cooking gas. He turned to his friends and, according to Raju's statement to the police, said: "Let's go out and have some fun."

Delhi's sclerotic roads. Photograph: David Levene for the Guardian

The men headed for the bus, which was parked 100 metres or so away on a side road, the statement says. On the way, they called on friends in the slum to join them. Two did: Pawan Gupta, a 19-year-old fruit seller and student, and Vinay Sharma, 20, who worked part-time in an expensive gym as a cleaner-cum-instructor. Both lived with their parents and had marginally more stable backgrounds than the others but were still far from exceptional in any obvious way.

Gupta, a relative said, had grown up in a temple in the remote rural town of Basti in north-eastern Uttar Pradesh, another desperately poor part of India. He had given up further education to come to Delhi to help his parents run their fruit stall. Still only 20, he was hoping to go to college. He had "fallen in with the wrong sort", a relative said.

Sharma, the son of an airport cleaner, was doing a distance-learning college course in communications and gave his parents the rest of the 5,000 rupees he earned each month at the gym catering to Delhi's elite a few miles away. Such a stark proximity between the very wealthy and the less well-off, between the aspirant and the arrived, is also typical of the new India.

Driven by Mukesh Singh, the bus first headed north-east, along Delhi's choked, congested inner ring road. The city has two such routes, both haphazardly planned and often gridlocked. The men pulled up at designated bus stops, where one of them – Raju, according to police – called out for anyone wanting a ride to Nehru Place, a shopping centre and office complex a few miles away. It was already dark and cold.

Badri Nath, left, father of the gang-rape victim, and her brother Gaurav at a press conference. Photograph: Mail Today/India Today/Getty

After about 10 minutes and several attempts to attract custom at different bus stops, a carpenter on his way home from work got on. Ram Singh shut the doors immediately behind him, and his brother accelerated away. Within minutes, the man had been beaten and robbed of his phone and 1,400 rupees, then dumped from the moving vehicle. He did not bother reporting the crime.

By 8.30pm, after another few abortive attempts to lure passengers aboard, the bus pulled up at a stop in a suburb called Munirka. To make the trap more effective, Sharma, Gupta and Thakur sat on different seats at the front of the vehicle, posing as passengers, and visible from outside through the open doors. Raju stood on the step of the bus. "For Palam crossing and Dwarka sector one," he shouted.

Work like a horse, live like a saint

Drive into Dwarka and the ragged reality of India's journey to prosperity is very obvious. A narrow flyover takes a stream of vehicles over a railway where packed trains pass slowly between strips of wasteland strewn with rubbish, faeces, and thin-ribbed cows. Everywhere there are people: labourers streaming from their makeshift huts to work on a series of unfinished, skeletal luxury flats that will be sold to the newly wealthy; women buying or carrying baskets of vegetables; schoolchildren in neat uniforms; young men doing little except play with their mobile phones; some beggars. Above soar billboards, advertising a conference with a "real estate guru", a "women's day" at a local gym where "cut-price classes" will "make him love your curves", and one poster composed of vast portraits of Mohandas Gandhi, Jawaharlal Nehru and the former president APJ Abdul Kalam, the "father" of India's nuclear programme.

One of the most striking elements of the Delhi gang-rape case is the similarity in the backgrounds of the victim and of her killers. The family of "J" – it is illegal under Indian law to name a rape victim – were, like those of her assailants, from close to the bottom of India's still tenacious caste hierarchy. Her father, Badri Nath, like the Singh brothers' father, had left his remote ancestral village for the capital in search of a better life. In 1982, a bus took him from his village on the banks of the Ganges in the middle of India's northern plains to a station where he bought a ticket for an overnight train to a city he had never seen. "I didn't want to leave," he said simply.

But he had little choice. Badri Nath was one of four brothers. The two eldest had been educated but funds were short and insufficient for Badri Nath to finish his schooling. His father was the only son of a man who himself was one of four sons. The family land, once enough to support a number of families, had thus been divided so many times that it was insufficient to provide a living even for one. Three years after he left the fields behind, his wife, who married when she was only 15, came to join him in Delhi.

Waiting for a bus in Delhi in front of an ad for the city. If life in the capital is better than village poverty, the gains for many have been marginal. Photo: Kevin Frayer/AP

In the city, Badri Nath managed to keep food on the table and a roof over the head of his young family. This was no mean achievement. In the mid-1980s, the Indian economy was still weak. The country was apparently locked into the "Hindu growth rate". Communal violence was rife, opportunities few. He started polishing pressure cookers, then worked in a washing machine factory. A sympathetic boss gave him money for a small plot of land in what was then the semi-rural suburb of Dwarka and he built a very modest, cramped two-room home there. He took on a second job as a night watchman in a hospital.

Slowly, over the years, the district developed. Electricity was connected, though problems with water supply never seemed to be resolved. More and more people flowed in from the rural areas. A decade passed, then another. Dwarka turned into a small town, then a small city, one of the many that fuse with the metropolis of Delhi itself. Economic development, accelerating steadily as the years passed, meant a newly monied middle class, and new airlines to take them to business meetings and beaches.

Delhi's airport expanded. New workers were needed, and Badri Nath, through a friend, found work as a loader, emptying planes he would never fly in of baggage as they came in from Mumbai, Bengaluru, Pune, Kolkata or elsewhere. He signed up for two eight-hour shifts, each one earning 100 rupees. He left home at 1pm and got home at 6am. The journey to work took 15 minutes in an unlicensed taxi, often vehicles driven by chauffeurs making some money on the side after dropping their employers off at the airport. Getting home took half an hour in an overcrowded bus.

"I heard once that to escape poverty you need to work like a horse and live like a saint," Badri Nath said later. "That is what I have tried to do all my life."

Interactive: the events of 16 December 2012. Click on the image to launch it

His first child was a boy who died after three days. In India, sons are prized to the point where they receive not only scarce financial resources for their education but also better food. Female foetuses are selectively aborted so frequently that Delhi and the states around it suffer a massive demographic imbalance between men and women. Badri Nath thought differently, however. "My wife was so sad when we had another child, we did not care if it was a boy or a girl. We just wanted it to survive," he said. The child was J, and she was followed over eight years by two boys.

All three children went to the local government school, but it was J who stood out. "She just needed to look at something once and she remembered it," said Badri Nath. Her textbooks lined a wall in the small home. To give her space to study and sleep, the rest of the family ate and slept in the second bedroom, covering a bed with a plastic sheet to convert it into a dining table.

"The only thing that interested her was studies," her father remembered. She covered the wall of her room not with Bollywood posters or pages from magazines but diagrams laboriously copied from her textbooks. Her handwriting and written English were soon the best in the family – her parents still conversed in the Bhojpuri language of their part of Uttar Pradesh – and it was J who filled in all the myriad administrative documents that blight every Indian's dealings with government. If there was any time left after studying, she helped neighbour's children in exchange for a few rupees or watched television on the family's cable connection.

She had wanted to be a doctor, ideally a neurosurgeon, but opted instead for the more modest, and more affordable, ambition of physiotherapist and found a college in the northern city of Dehradun where she could qualify after a four-year course. To raise the 40,000-rupee annual fee, her father sold part of his land in his village and mortgaged the rest. To cover living expenses – a similar sum – J found a job in a call centre in the city.

It was through a mutual friend at the call centre that she met Awindra Pandey, the 28-year-old information technology specialist who was with her on the night of the attack. The two were "just friends", J's father said, though he often spoke to the young man on the telephone and liked him. There was no question of the pair marrying as they came from different sides of what, in India, remains an unbridgeable gulf.

Pandey's family were from the upper castes and his father was a wealthy lawyer. He had a good salaried job – only a quarter of working Indians are employed in the formal sector – as an IT specialist. But if there would never have been a match, there could at least be companionship. The couple had been seeing each other for over a year and had even been on a trip to the hills together. They had not seen each other for more than month however before the attack. It was J, back in Delhi to look for an internship as a physiotherapist, who called her friend to suggest a trip to the cinema. Pandey picked her up from home and they travelled to Saket Mall, an upmarket shopping centre in the south of Delhi, where they watched Life of Pi at a multiplex, leaving at about 8.30pm. They walked out past the western-branded clothes shops and supermarkets, the new coffee bars, the car rank where drivers pull up in imported 4x4s, which they then load with shopping as their employer settles on the back seats, past the uniformed security guards, into the darkness of the evening, and started looking for transport home. This was a different India from that which J's father had known.

Women light candles in memory of J at an impromptu shrine in Delhi. The brutal crime triggered unprecedented protests, even as subsequent rapes pushed the student's death off the front pages. Photograph: EPA

Jugaad

Delhi's public transport is grossly inadequate at the best of times. If the reforms of the 1990s unleashed the power of the private sector, for good or ill, they did little to bolster the public sector. Since, public services and institutions, under increasing pressure, have not just failed to keep pace but have often in effect collapsed. So even a new and expanding metro in Delhi has barely made a difference in the seething city. As ever in India, where the state fails, jugaad ("frugal innovation") takes over. Unlicensed buses are broadly tolerated, or at least allowed to run, after paying a small bribe to avoid a fine.

On this Sunday night there were no official Delhi Metropolitan Corporation buses to take J and Pandey back to Dwarka. No auto-rickshaw wanted such a distant fare either. The couple convinced one driver to take them two miles from the mall to another bus stop, at Munirka, where they hoped to find more options to get back to Dwarka so Pandey could see J safely home.

According to Pandey's statement to police, the couple had been waiting only a few minutes when the bus driven by Mukesh Singh pulled up with the juvenile leaning from the open door calling out its destination. "Where are you going, didi?" he asked the woman, using the colloquial Hindi for elder sister, police statements say.

The couple got in and sat down, falling for the ruse that the men posing as passengers had prepared. "How long will it take?" Pandey asked. "Not too long," replied Ram Singh. His brother, Mukesh, was still at the wheel. One of the other men, still playing his role, asked the same question. "Let's get going," Ram Singh said as his assistant Thakur took 20 rupees as a fare from the couple. The bus moved off.

Within minutes, as the bus drove along Delhi's outer ring road in the direction of the international airport, the atmosphere darkened.

"What are you doing out roaming around with a girl on her own?," Ram Singh asked Pandey, according to the accounts given to investigators by both the juvenile and the man. "None of your business," the young IT engineer answered. The two men faced off. Ram Singh threw a punch. Then events moved very fast. Ram Singh and the others wrestled Pandey to the floor. One shouted: "The rod, [get] the rod." As the woman screamed for help, banging on the bus's curtained windows, a metal bar kept in the bus was passed back. Blows rained down on the helpless man, now pinned between two seats. He was stripped. "I was trying very hard to get to her but they had me nailed down," Pandey later told a magistrate.

As Mukesh Singh drove the bus through the heavy traffic, Thakur and Ram Singh had dragged the woman to its back seats, according to the men's statements to police after their arrest. "They beat her and pressed a hand over her mouth and tore her clothes off," the juvenile's statement says.

"Ram Singh first raped her, the girl kept shouting, and one by one all of us [raped her] and [Ram Singh] and the rest of us bit her body." Medical reports reveal bite marks were found on the woman's breasts, arms and genitals. J fought back, biting and scratching but the petite young woman had little chance.

Outside the bus, the landmarks of south Delhi passed: a temple, a flyover, a busy road junction. At Mahipalpur, a scruffy collection of cheap hotels and restaurants near the airport, they turned the bus round, heading back into the city. It was 9.34pm, according to CCTV images. The vehicle had passed through three police checkpoints, where officers from the city's overstretched, badly paid, badly trained and badly equipped force stood supposedly keeping an eye on passing traffic.

As the bus headed back into the city, the attack continued. Ram Singh exchanged places with Mukesh who had been driving. His brother then took his turn to rape the woman.

"We tried to push our [penises] into her mouth. We also tried to [sodomise] her," the juvenile later told police. His statement, corroborated by the account given by the victim to medical staff, does not mention the assault with the iron bar the woman described. Her medical examination – and the retrieval of two blood-stained rods in the bus – confirm that it was penetration by this that caused massive damage to her genitals, uterus and intestines.

"The girl was shrieking and shouting so much. Ram Singh put his hand inside her and pulled out flesh. The girl lost consciousness and started bleeding," the juvenile told police. Her friend later described how, naked and badly injured himself, he heard the men talking. One said that he thought "she was dead". Another, possibly Thakur, suggested throwing them out of the bus.

By this time – at exactly 9.54pm, according to images recorded by cameras – the bus had turned around once again and had returned to Mahipalpur. The men dragged their two semi-conscious victims, by the hair according to police documents, to the rear doors of the vehicle but these were jammed shut so they pushed the couple through the front doors. An attempt appears to have been made to run them over, but Pandey, though badly injured, was able to drag the woman out of the way. The bus then disappeared into the traffic and back into the city.

When they reached Ravi Das Colony, the men parked the bus down a nearby alley. With water fetched from one of the colony's two standpipes, they sluiced it down with water to get rid of the blood, faeces and other evidence. They lit a fire, burning the clothes of the couple, except for the man's Hush Puppies shoes, which they kept.

The six then went back to the Singh brothers' home, where the juvenile made tea. Ram Singh divided up the results of the night's robberies, distributing credit and bank cards, cash and mobiles, jewellery and the shoes. Gupta got a wristwatch and 1,000 rupees, the juvenile was given 1,100 rupees and a bank card. "Keep it carefully," Ram Singh told him. "We'll take out the money later."

There was a brief argument, overheard by neighbours. The two men, Gupta and Sharma, who lived elsewhere in the colony, went back to their houses. The others watched television and then slept, investigators say.

Mahipalpur

Mahipalpur is, like Dwarka, Trilokpuri and Ravi Das Colony itself, another place of transition, another scrawled note on the margin of the story of India's growth. Supposedly in Delhi's "green belt", it had once been where sultans had hunted. Only a few decades ago it was still a small village, surrounded by scrubby, rocky hills and small pools of water where buffaloes bathed in the summer, submerged up to their necks to fight the heat.

Now it is a noisy crossroads where the road to Delhi's airport joins a six-lane highway leading to the satellite city of Gurgaon, favoured by big international companies. Scores of unlicensed cheap hotels and restaurants cater to the passing trade of late-night arrivals from overseas, commuters heading in or out of the metropolis, lorry drivers and well-off teenagers driving their fathers' fast cars looking for a plate of chilli chicken at 5am.

For 40 minutes after their attackers had driven away, J and her friend lay, drifting in and out of consciousness, on a narrow strip of wasteland beside a slip road of the highway. A few hundred metres away, across open ground, the sign of a French-owned budget hotel under construction shone in the darkness. On the other side of the road, beyond the flyover, was a row of hotels. Lying in the gravel, bleeding heavily, they were nonetheless visible to the traffic streaming past. Vehicles slowed, almost stopped and then accelerated away, Pandey later remembered.

Eventually, as ever in India, a small crowd gathered, though no one wanted to take responsibility for actually helping the naked and injured couple lying on the ground. Finally, according to police documents, an off-duty worker on the nearby toll highway saw the bystanders, stopped, and alerted his control room, which notified the police. A constable arrived in a patrol car, then another. One fetched a sheet from a nearby hotel to cover the couple. There was a brief discussion over which police district was responsible for dealing with the situation. Then Pandey helped J into a police car and was driven away.

Police fire water cannon at protesters demonstrating at Delhi's India Gate over the government's reaction to the gang-rape. Photograph: Daniel Berehulak/Getty

An hour later, a policeman called J's father to tell him his daughter had been in an "accident" and was in a hospital in south Delhi. A friend with a motorbike took him across the city to Safdarjung hospital, one of Delhi's biggest public medical facilities. He found her lying on a stretcher, covered by a green blanket.

"I thought she was unconscious but when I laid my hand on her forehead she opened her eyes. She was crying. I told her: 'It'll be alright, beta [child].'"

Doctors had been appalled at extent of the woman's injuries. They attempted to remove the most damaged parts of her intestines and any infection, cleaning as much as possible of what was left and doing whatever else they could to keep her alive. But there was little hope, they all knew. One found her father, who had been waiting outside the operating theatre, and told him that it was unlikely his daughter would survive more than a few hours.

Through the morning, police worked at tracing the white bus that Pandey, badly hurt but still conscious, had been able to describe to them. They started checking CCTV footage from the hotels clustered around Mahipalpur. One noticed a bus with the name Yadav painted on the side, which passed the crossroads twice an hour before the couple had been reported. They found its owner, who had bribed local officials after being repeatedly caught running unlicensed fleets, and got an address for Ram Singh.

At Ravi Das Colony they first saw the bus, then Singh sitting inside. He ran but was caught. His T-shirt and shoes were bloodstained. The bus had clearly been washed recently. Very quickly, Singh admitted his involvement in the attack, even producing two iron rods, covered in dry blood, from a compartment in the bus's cabin. By the end of the week, five of the six were in custody. Mukesh Singh had been detained on his way to Karauli, where he hoped he could hide in the remote village where he had grown up. Gupta and Sharma were found at their family homes in Ravi Das Colony. Raju was picked up at the bus station where he slept. Thakur was found when he arrived at his parents' home in remote Bihar. By then, news of the incident was not just leading every bulletin in the city, but across India.

It had long been known that Delhi had a problem with sexual violence. Statistics backed up anecdotal evidence. For years, every few days, the media reported a serious sexual assault, though usually tucked away on the metro pages and recounted in a few dry paragraphs. Every few weeks there would be an attack, often a gang-rape. Some would receive more attention. But after the expressions of concern by police officers and Delhi's elected officials the issue would soon disappear. Few of the incidents ended in charges, almost none in a trial. The conviction rate for rapes languished around the 25% mark.

According to India's National Crime Records Bureau, registered rape cases in India had increased by almost 900% over the past 40 years, to 24,206 incidents in 2011, while murder cases had gone up by only 250% over 60 years, and incidences of riot had actually dropped. Delhi, with its population of 15 million, registered 572 cases of rape, compared with 239 in Mumbai, India's commercial capital, with its bigger population, in 2011. There were just 47 reported in Kolkata.

But no one knows quite what proportion of attacks these figures represent. Some activists say one in 10 rapes are reported; others say it is probably more like one in 100. One poll, in 2011, found that nearly one in four Indian men admitted to having committed some act of sexual violence. Two-thirds of the sample came from the capital.

Then there is the daily low-level harassment in public places, simply accepted as part of life in the city. Suggestive comments and wandering hands on buses, photographing or filming with phones, being followed or even chased were, polls showed, regularly encountered by 80% of women in the city. According to one survey, this molestation – euphemistically known as "Eve-teasing" – was seen as harmless by a majority of men in Delhi. An investigation by Tehelka, a campaigning magazine, found that the policemen supposed to investigate "Eve-teasing" and rape alike blamed women for "leading men on".

A high proportion of Delhi's police are recruited from the surrounding rural areas and the big, poor conservative states of Uttar Pradesh, Bihar, Haryana and Rajasthan. Their attitudes inevitably reflect those of their home communities. These are very similar to Karauli, Aurangabad, Trilokpuri and the other places where J's attackers had grown up or spent many years. Only two months before the Delhi attack, a spate of rapes and gang-rapes in Haryana prompted some debate in the media. Local politicians attributed the wave of attacks to women behaving immodestly or the amount of junk food young men were eating. One called for the age of marital consent to be lowered. The United Nations pointed out that this would do little to counteract the rape of teenagers. These states are also the parts of India where gender imbalance owing to selective abortion is worst. Violence to women starts before birth, campaigners often say.

But J's case was exceptional, standing out from the mundane background hum of sexual violence in northern India. The attack was of almost unprecedented brutality, committed by complete strangers on a Sunday evening, on the streets of Delhi itself. J was out with a friend watching a film. She was not in a village, nor was she working in a nightclub. She was thus seen as representative in a way that other victims, rightly or wrongly, had never been. Very soon she had been dubbed "Delhi's daughter" in the media, and thus neatly slotted into one of the three legitimate categories allowed to women in India: mother, spouse or child.

Within hours of the news of the assault breaking, protesters were on the streets. The reaction of India's political elite merely fuelled the anger. No parliamentarians joined the marchers. Instead, the government invoked colonial-era laws to ban demonstrations, shut metro stations and deployed thousands of policemen to guard the president's residence, the parliament building and the homes of senior ministers. Central Delhi became a citadel, defended by khaki-clad men with lathis, the iron-tipped bamboo staves also inherited, like the attitudes of the ministers and top bureaucrats, from former imperial overlords. Finally, after a week, the prime minister, Manmohan Singh, and Sonia Gandhi, president of the ruling Congress party, made brief televised speeches expressing concern and sympathy, which were dismissed as too little, too late by protesters. The anger grew.

On 25 December, having held on to consciousness for long enough to twice give a crucial statement to investigators, J, still in Safdarjung hospital in the south of Delhi, began to lose her grip on life.

Her father, Badri Nath, said: "During the evening, maybe 9pm, she saw me standing outside the intensive-care unit. She turned to look at me and gestured for me to come. She asked me if I had eaten. I said yes. Then she said: 'Dad, go to sleep, you must be tired.' I patted her head.

She said: 'You should get some sleep,'" he remembered. "She took my hand and kissed it. She never opened her eyes again."

Four days later, J died in a clinic in Singapore, where she had been moved as no facilities for treatment that would even give her a chance of life existed in India. Her body was brought back to India, cremated in a public facility in Dwarka and then, as is traditional, her ashes were carried by her family to the banks of the Ganges, near the village that Badri Nath had left 30 years before, and scattered on the river.

The night of her death the angry protests that had been beaten back by riot police in central Delhi and the marches in other cities demanding security for women in India gave way to demonstrations of a different type. There was grief, even shame. At 7pm, candles were lit across the vast country: on Juhu Beach, where Mumbai meets the Indian Ocean; in the centre of the bustling southern cities of Hyderabad and Bengaluru; at the statue of Gandhi in chaotic, poverty-stricken Lucknow, 1,000 miles to the north.

In Delhi itself, though a city full of temples, mosques and churches, scores gathered at an impromptu shrine set up at the bus stop where J had waited for a lift home 13 days before. Under the hastily printed posters reading "You Inspired Us All" and "No to Violence to Women", they too lit their candles. "We are feeling very sad. We are feeling very angry. Now we hope our lives will change," said Archana Balodi, a 24-year-old student. One poster read: "She is not dead, she has just gone to a place where there is no rape."

At the Jantar Mantar, an 18th-century observatory that is a traditional site of protests in the centre of the city, crowds gathered. J's death meant her attackers would now be charged with murder, and thus could face hanging. This became the cry that united the otherwise diverse and disorganised demonstrators. "Hanging them is not enough. They should be tortured like she was," said Srishdi Kumar, a 16-year-old schoolgirl. "Then maybe there will be a change. Why not?"

Eight months later, at the conclusion of the trial of her killers, it is difficult to argue that J's ordeal and death has made much difference in India, at least so far: the rapes and sexual assaults that are now highlighted daily by the Indian media act simply as a reminder of how widespread violence to women is in the country.

The fierce debate in the weeks after the attack – setting conservatives who blamed westernisation against liberals blaming reactionary sexist and patriarchal attitudes – has faded. A package of laws increasing punishments for sexual assault and redefining a range of offences may do some good, campaigners concede, if enforcement is simultaneously improved, but dozens of men accused of rape remain members of local and national parliamentary assemblies. The special funding released by the government for measures to enhance the security of women has so far gone unspent. Few are confident that gender training for the underfunded police will have much effect. Nor are the new "fast-track courts" – such as the one, only a few hundred metres from the mall where J and Pandey watched Life of Pi, where her attackers were tried – solve the problems of the criminal justice system. "It is a few weeks of outrage against hundreds of years of tradition," MJ Akbar, a veteran commentator, said. But this may not be so. The concern is that it is the change itself that is generating the violence.

The trial has now ended. Ram Singh, the ringleader in the attack, hanged himself in his cell in Tihar prison in mid-March. J's family angrily cried that they had been denied justice. "It is wrong that he should be able to choose the timing of his death," said her brother. The other four adults who have been convicted are likely to be hanged after all appeals are exhausted. No one is quite clear what will happen to Raju, the juvenile, though he may have to be released after three years' time in a juvenile reform home.

Badri Nath, his wife and two sons have now moved to a new flat with running water, electricity and two bedrooms, a gift from the Delhi authorities. The family has also received "compensation payments", in the cold language of the bureaucrats, worth £40,000: more than Badri Nath could have ever hoped to have earned, let alone saved, in his working life. His sons are getting coveted government jobs. In a recent interview with the Guardian, he repeated one phrase: "I console myself by saying she was a good soul, set free in death."

Outside in the narrow street, a tanker had just arrived to deliver water. Dwarka's piped supply is still unreliable. A crowd had formed and neighbours argued as they jostled with buckets. A woman laughed. A motorbike clattered past. A vegetable seller shouted for custom. There was a short burst of music from a tinny radio. But the noise of an evening in a working-class Delhi neighbourhood barely reached the small basement flat where a 53-year-old man sat on his daughter's bed, and it was very quiet

• This article was amended on 16 September 2013. An earlier version of the graphic showing proportions of girls and boys was the wrong way round.