British police said Saturday they had charged a man arrested after a refrigerated truck was found earlier this week with 39 bodies inside with manslaughter and people trafficking.
Maurice Robinson, 25, from Northern Ireland, faces "39 counts of manslaughter, conspiracy to traffic people, conspiracy to assist unlawful immigration and money laundering", police said.
Vietnamese citizens are feared among 39 people found dead, families and community organisers said on Saturday, after the tragedy laid bare the risks of illegal migrant routes to Europe.
British police initially said all 31 men and eight women found in a lorry in an industrial park in Essex this week were believed to be Chinese.
But several Vietnamese families have come forward saying their relatives went missing on route to Britain, a prime destination for Vietnamese migrants seeking better lives abroad.
All of the families come from impoverished and remote corners of central Vietnam, a hotspot for migrants embarking on dangerous journeys and lured by promises of earning quick riches overseas.
Many are smuggled illegally through Russia or China, often indebted tens of thousands of dollars and carrying falsified documents, and end up working off the books on cannabis farms or in nail salons.
Five people have been arrested in the UK in connection with the tragedy, which sparked the largest murder probe in Britain in almost 15 years.
Several families told AFP Saturday they feared their relatives were among the dead.
In central Ha Tinh province, the father of 20-year-old Nguyen Dinh Luong said he received a call from a Vietnamese man in the UK this week saying his son had died en route to Britain.
"I fell to the ground when I heard that," Nguyen Dinh Gia said. "It seemed that he was in the truck with the accident, all of them dead."
Britain-based community group VietHome said it had received "photos of nearly 20 people reported missing, age 15-45" from Vietnam.
The truck carrying the migrants arrived in Purfleet on the River Thames estuary on Wednesday, on a ferry from the Belgian port of Zeebrugge.
British police refused to confirm if any of the victims were Vietnamese Saturday, after all the bodies had been transferred to hospital for autopsies.
But a senior officer said he had met with Vietnam's ambassador to discuss how to fast track the process of finger print identification and DNA testing to identify the victims.
Vietnam's Prime Minister on Saturday called for government agencies to help establish victims' identities and look into illegal migration.
Police did not rule out the possibility that the victims could have been trafficked into the UK by "criminals".
"We've got to be realistic. We know that... we have people coming into the country, either being trafficked or as asylum seekers," Detective Chief Inspector Martin Pasmore told reporters.
"It must be clear that criminals - and that's what we're dealing with, criminals, murderers - are taking more and more chances with these vulnerable people," he added.
An Irish man in his early 20s was arrested on Saturday in connection with the incident, police said.
The driver of the truck, a Northern Irish man, was arrested at the scene, while three others were arrested on Friday.
Among them was a woman named as the legal owner of the truck, and her husband. They denied any involvement, according to media reports.
The police investigation is Britain's largest murder probe since the 2005 London suicide bombings.
Families of missing Vietnamese migrants on Saturday held vigil and set up makeshift altars in their homes in central Nghe An province, where many of the suspected victims came from, praying for news from missing relatives.
On Friday, the first indications emerged that victims might be Vietnamese instead of Chinese, as earlier identified by British police.
The family of a 26-year-old Vietnamese woman, Pham Thi Tra My, said they received a chilling text message from her in the hours before she is believed to have died.
"I'm sorry Mom. My path to abroad doesn't succeed. Mom, I love you so much! I'm dying because I can't breathe," she said in the message confirmed by her brother Pham Manh Cuong.
Their home province of Ha Tinh was devastated by a massive fish kill in 2016 when a Taiwanese steel firm dumped toxic wasted into the ocean.
The disaster wiped out livelihoods in the coastal area and experts say it may have led to an uptick of illegal migration from the region.
Migrants can pay smugglers up to $40,000 for the dangerous journey, an enormous sum in Vietnam, where the annual per capital income is around $2,400, according to the World Bank.