The mango trees lie on the edge of the village, offering sanctuary from the bitter sun of the north Indian plains. A shelter, a playground, even a shrine for some, they are now a place of death.

This weekend the trees and the parched fields around them are a crime scene, trampled by local officials, politicians who scent a vote-winning cause, policemen with ancient Lee-Enfield rifles, fast-talking Indian TV reporters and a stream of onlookers from other villages. All stare at the branches of the largest tree, from which two girls were found hanging at dawn last Wednesday, hours after they were abducted and gang-raped. The cousins, aged 14 and 15, had disappeared the night before and were last seen being hauled across the fields by three local men.

The crime was the latest in a series that has shocked India and badly damaged its image overseas. It combines many of the most tenacious problems in this fast-changing but troubled country: embedded social hierarchies built on prejudice, ritual and violence; huge inequality; patchy and politicised policing; and violence to women.

Government statistics show 244,270 offences against women reported to the police in 2012 in this nation of 1.25 billion. But campaigners say that this, a 6% rise on 2011, is only a small fraction of the total of such crimes.

In the village of Katra Sadatgunj, a backbreaking seven-hour drive over 200 miles of rutted roads from the capital Delhi, police officials stress that "steps will be taken". "Now there is tension, but it is temporary. The situation will be normalised," said Superintendent Maan S Chouhan, in charge of day-to-day policing in Badaun district, one of the poorest parts of one of the most deprived states in India.

But the situation will not normalise for Sohan Lal, a farmer who says he is around 50 years old and has lived in the village all his life. At dawn last Wednesday he found his daughter and her cousin hanging from the tree. Talking to the Observer in the family's earthen-walled house, he pointed to the mud stove where his youngest daughter, who cannot be named under an Indian law to protect rape victims from social stigma, used to cook dinner when she returned from the village school. "She was always studying and working. That's what she liked best. She wanted to be a doctor," he said.

Neighbours confirmed the picture of an earnest, modest young woman. "She was very quiet and never in trouble,' said Narendra Kumar, 21. "Some boys and girls around here exchange texts and so on, though we can't really meet in the open much. But she didn't."

Her best friend was her cousin. On Tuesday night the pair set off into the fields just after dusk. Few Indian villages have proper sanitation, so half the country's population use fields instead. For women this poses particular problems, as strict traditions on modesty mean they can only go in the dark. This leaves them vulnerable to harassment.

A further factor put the two teenagers in greater danger. Katra Sadatgunj is a Dalit village, meaning it is home to a community from the lowest ranks of the Indian "caste" hierarchy. Dalits, formerly known as "untouchables", still face systematic discrimination across India. Though in urban areas "caste" identities are weakening, they are still strong in rural areas and particularly in northern parts of the country.

When the girls failed to return, Babu, Lal's brother, went out to look for them. There is little electricity in Katra Sadatgunj, – perhaps for an hour a day at best and then only a weak current – so the village was in darkness. But Babu found them by torchlight as they were being pulled and pushed by three local men, aged in their early 20s. He backed off when one threatened him with a home-made handgun, he later told the Indian Express newspaper.

Of those who reported rapes in India in 2013, 98% named parents, relatives and neighbours as the accused. The men seen by Babu were neighbours, living just 100 metres from the mango trees on the edge of the village.

But they were from the Yadav caste, still low in the hierarchy but higher than the Dalits and powerful in the village. The area is demographically dominated by Yadavs, the state government is run by a Yadav family and the police in the village were Yadavs. Dalits are often landless labourers, dependent on employment offered by small landowners from higher castes. "What can we do? They are powerful. We are not. They lord it over us," said Lal, the bereaved father.

One teenage boy in the village described how attempts by Dalits to defend their unmarried sisters usually ended in a "thrashing". Chouhan, the policeman, described it differently: "Relations are happy and healthy between communities ... They help each other with agriculture."

Lal said that when he went to the local police station, staffed by Yadavs, they refused to investigate, asking him his caste. Four hours later he received a call from another officer, telling him to "go to the mango trees, the body of your daughter is there".

The girls had been hanged, suspended by the cloth, pink for one and green for the other, they used as headscarves. Postmortems showed they had been repeatedly raped, but doctors were unable to establish, officials said yesterday, if they had committed suicide or been hanged.

One senior officer, requesting anonymity, suggested the families of the dead girls might have murdered them on learning of the "shameful" gang rape. Such "honour killings" do occur in northern India, and though there is no evidence to back the claim many locals appeared yesterday to have assumed this was one. "They did the right thing, the family. Absolutely," said Jitender Saath, 22, from a neighbouring village.

Much of the attention in India has focused on the failings of the police. Those from the village who refused to search for the girls – one is implicated in the rape – are now in jail and have been dismissed from the service. The conviction rate for rape in India is relatively high – around one in four of cases that make it to court. The three neighbours have now been detained.

Legal changes introduced after the gang-rape and murder of a 23-year-old physiotherapy student in Delhi in December 2012 have made rape a capital offence. Mulayam Singh Yadav, a heavyweight politician in Uttar Pradesh and member of the national parliament, said this was too harsh, because "boys will be boys … [and] make mistakes".

The 2012 Delhi gang-rape provoked widespread anger and an unprecedented debate on the causes of the wave of sexual violence in India. Some pointed to a clash of urban and rural lifestyles, to Bollywood films, to the country's skewed sex ratio. A series of reforms appears to have made little difference in places like Katra Sadatgunj.

Yesterday Rahul Gandhi, vice-president of India's Congress party, visited the village and spoke to Lal. "He spent about 10 minutes here," said the farmer. Afterwards "he promised he'd get me justice. Let's wait and see."