Along the India-Bangladesh border that runs through India's eastern state of West Bengal, human traffickers are buying land, building homes and enrolling on voter lists to create cover for their cross-border operations, campaigners said.
"Traffickers operating in border areas are constantly looking for ways to legitimise their business," said Adrian Phillips of non-profit group Justice and Care, which works on the prosecution of traffickers and care for victims.
"Purchase of land using fake documents is ... carried out to gain a foothold, establish support, a base and build a nexus."
Thousands of people – largely poor, rural women and children – are lured to India's towns and cities each year by traffickers who promise good jobs but sell them into prostitution or domestic servitude.
West Bengal state – which shares a porous border with poorer neighbours Bangladesh and Nepal and is a known human trafficking hub for that reason – registered more than one-third of the total number of victims in 2016.
A report by Justice and Care and the Indian Border Security Force last month points to specific instances where traffickers on both sides "cement their operations" by buying land in villages close to the India-Bangladesh border and enrolling their names in voters lists in the village councils.
The porous, roughly 2,000km long border running through West Bengal is demarcated primarily by border pillars and meanders through villages, agricultural land and rivers.
Every day it is crossed by thousands of people, who share similar ethnic, religious, linguistic and cultural characteristics.
These features along with the topography make it easy for infiltrators, smugglers and human traffickers to cross over into India, security officials say.
"When traffickers produce valid voter cards or land deeds, it makes surveillance and identification even tougher," a senior Border Security Force officer told the Thomson Reuters Foundation, declining to be named.
India – which has an estimated 40% of almost 46 million people enslaved worldwide according to the 2016 Global Slavery Index – is a destination and transit point for young girls and women being trafficked into brothels or domestic servitude.
Traffickers are using fake documents to buy land or acquire Indian identity cards, the report said.
It gave the example of "Trafficker 1", a Bangladeshi citizen who had all the necessary Indian identity documents, including a ration card.
He had purchased government-owned land and built a house on it, using it as a temporary shelter point for girls being trafficked from Bangladesh. The researchers discovered that more than 35 girls trafficked by the person were working in Mumbai.
Describing their journey from their villages in Bangladesh to brothels in India, most trafficking victims said they were "harboured" for a night in a shelter along the border.
These mustering points are grooming grounds for the girls who are to be sold to brothels later, the report said.
"We are acutely aware of the issues arising from a person having a fake voter card because that is proof of Indian nationality," said Antara Acharya of the district administration of North 24 Parganas, a border district in West Bengal.
"It's not easy when the international border divides a village in two in certain parts but we take up every complaint that comes on a priority basis."