BRUSSELS (AP) — Police in Belgium and France on Wednesday announced the arrests of 26 people suspected of human trafficking in the deaths of 39 Vietnamese migrants who were found in a refrigerated truck in Britain last year.

Judicial authorities said a series of early morning raids took place simultaneously in Belgium and France on Tuesday as part of two legal investigations.

One inquiry was launched following the investigation into the deaths of the 39 migrants found in October inside a truck's refrigerated container that had been hauled to England.

Police investigating the case found the 31 male and eight female victims were all from Vietnam and ranged in age from 15 to 44, including three minors.

Police said migrants died from a combination of a lack of oxygen and overheating in an enclosed space. The victims came from impoverished villages in Vietnam and are believed to have paid smugglers to take them on the risky journey to better lives abroad.

Last month, the truck driver pleaded guilty to manslaughter at a London court.

In Belgium, the federal public prosecutor’s office said the investigation quickly established the route taken by the victims before they got into the truck and said some of them had stayed in Belgium before their departure.

Tuesday's large police operation was organized with a trans-border investigation team coordinated by the European Union crime agency Eurojust that included Belgium, France, the U.K and Ireland.

The Paris prosecutor’s office said the 13 people arrested in France are suspected of taking part in a criminal organization that had been housing and transporting several dozen migrants from Southeast Asia every day for several months.

Sixteen searches took place Tuesday in the Brussels area, including in safe houses, leading to the arrest of 11 Vietnamese citizens and two Moroccans. Five of them have been charged with migrant smuggling with aggravating circumstances, belonging to a criminal organization and forgery.

Europol, the EU agency for law enforcement cooperation which provided support to the operation, said that 21 migrants were found during the raids.

“These criminal activities were particularly dangerous due to the life-threatening conditions of transportation," Europol said. “The urgent operational actions were crucial to safeguard particularly vulnerable victims and to arrest suspects at a high risk of fleeing."

The suspected smugglers face up to 15 years in prison and a fine of up to 150,000 euros ($162,000) per identified victim.