I believe international truck shipments are often sealed for security, to keep migrants from hitching a ride unbeknownst to the driver. The seal is broken if the doors are opened, to make it easier to see which trucks might be carrying people.
Some don’t even know they’re carrying anything other than what the manifest says; opening a container any place other than pickup, destination and inspection points means a loss of time and can be construed as tampering. In Spain we sometimes have cases of a truck driver noticing something funky with the load or with the way the truck handles and calling the cops (either him directly or his company), but that requires a driver who knows how that truck handles and a driver and company who take that kind of thing more seriously than they take missed deadlines or bonuses.
Essex Police has started extradition proceedings to bring a man from Ireland to the UK to face charges of manslaughter over the deaths of 39 people in the back of a lorry.
Eamonn Harrison, 23, from Northern Ireland, was arrested in Dublin on a European Arrest Warrant.