PARIS — More than two dozen people have been arrested in Belgium and France in connection with the deaths of 39 Vietnamese migrants whose bodies were found in a refrigerated truck in Britain in October, the authorities in both countries said on Wednesday.
Prosecutors’ offices in Paris and Brussels said the 26 suspects were believed to be part of broader human trafficking network that had transported not only those found dead in the truck but several dozen people a day for months.
Most of the trafficked migrants came from Vietnam, including the eight women and 31 men who crossed the English Channel in a container and were discovered on Oct. 23 in an industrial area of Essex, about 25 miles east of London, and not far from the ferry terminal where the truck had arrived from Belgium.
The discovery of the 39 victims, including three minors, prompted an investigation in four European countries that led on Tuesday to the arrest of 13 people in the Brussels area, and 13 others in the vicinity of Paris.
“The investigation quickly established the route taken by the victims before getting into the truck,” the prosecutor’s office in Belgium said in a statement released on Wednesday. “Some of them stayed in Belgium before their departure.”
None of the suspects have been formally charged, and they have not been publicly identified. The authorities in Belgium said 11 suspects were Vietnamese and two were Moroccan, and that they could appear before an investigating judge.
The 13 suspects in Belgium were taken into custody at safe houses where five migrants were also found, according to Eurojust, a European Union agency that helps coordinate judicial agencies across the bloc.
The French prosecutor’s office said most of those detained there were from France and Vietnam, and they can be held for up to 96 hours without being charged.
Many of the people who were found dead in October came from two impoverished provinces in north-central Vietnam, where some refer to those who leave for Europe as “box people,” a dark echo of the “boat people” who fled the country after the Vietnam War.
The trip that ended in tragedy in October took at least one of them from Vietnam to Russia, then Ukraine, and France — the country where smugglers “received, hosted and drove” most of their victims, according to the Paris prosecutor’s office — before they embarked on the final leg of their journey.
Vietnam, the British authorities have said, is one of the main sources of human trafficking victims into Britain, where they work in nail salons or factories, and face exploitation and abuse from organized trafficking gangs.
One of the victims, 26-year-old Pham Thi Tra My, was hoping to find a job as a manicurist in London, after her trip from Vietnam took her to Beijing and France.
“Mom, I love you and Dad so much! I’m dying because I can’t breathe,” she wrote in a text her mother in the early hours of Oct. 23, hours before the bodies were found.
As the authorities in France and Belgium pursued the case, the authorities in Britain and Ireland have moved against several people in recent months. The truck driver, 25-year-old Maurice Robinson, has pleaded guilty to 39 counts of manslaughter, conspiracy to traffic people, conspiracy to assist unlawful immigration and money laundering.
Another truck driver from Northern Ireland, 23-year-old Eamon Harrison, who is accused of having delivered the container to Zeebrugge, also faces charges including 39 counts of manslaughter. He is appealing against a request to extradite him from Ireland to Britain.
Ronan Hughes, a 40-year-old owner of a haulage company who is believed to have paid Mr. Robinson to drive the truck, was arrested in Ireland last month and faces 39 charges of manslaughter. The authorities have described Mr. Hughes as the ringleader, and are seeking his extradition to Britain.
The Belgian authorities said the people arrested on Tuesday faced up to 15 years in prison, and fines ranging from €1,000 to €150,000, or from $1,100 to $165,000, per identified victim.