A truck found in Essex this morning with 39 bodies inside is registered to an Irish owner.
Police in England now believe the refrigerated container travelled from Belgium, after being picked up by a lorry cab from Northern Ireland.
The driver of the truck, a 25-year-old man from Northern Ireland, has been arrested on suspicion of murder.
The container of the lorry was found in an industrial estate in Essex this morning.
Paramedics had been called to the scene, who then alerted police.
The bodies of 38 adults and one teenager were found inside.
Police expect their investigation will be "lengthy and complex".
"We continue to work with local partners and international authorities to gather vital intelligence and identify those who have sadly died", a statement read.
