Police in southeastern England launched a murder investigation on Wednesday morning after discovering 39 bodies in a box truck driven by an as-yet unnamed 25-year-old man from Northern Ireland. The driver has been taken into custody on suspicion of murder, but few other details have been made available thus far.

According to police, the truck was believed to have originated in Bulgaria, which is a member of the European Union along with Britain for the time being. However, it’s common for European trucking companies to be based in Bulgaria and use it for registration purposes due to its lower costs when compared to other nations on the continent. Indeed, Bulgarian Prime Minister Boyko Borissov has already claimed that the truck has not been in his nation since it was registered to an Irish woman in 2017.