Police are working to identify the 39 people found dead in the back of a lorry in south-east England as a wide-ranging murder investigation into the horrifying incident continues.
A man, named locally as Mo Robinson from Portadown in Co Armagh, Northern Ireland, is being held on suspicion of murder over the discovery in the county of Essex.
Officers searched two addresses in Northern Ireland as the force questioned the suspect after the bodies were found in Waterglade Industrial Park, Grays, early on Wednesday.
The searches in Co Armagh last night were believed to be linked to the arrest of the driver.
Detectives have said the trailer containing the victims arrived at Purfleet from Zeebrugge in Belgium at around 12.30am.
The front section of the lorry, known as the tractor, came from Northern Ireland, the force said.
The lorry and trailer left the port shortly after 1.05am and officers were called around 30 minutes later after ambulance staff made the grim discovery.
Several pictures on his Facebook profile match those of the vehicle at the centre of the investigation in Grays.
Eric Van Duyse, a spokesman for the Belgian federal prosecutor's office, said that Brussels had started an investigation into the incident.
He added: "We have no idea at the moment how long the lorry spent in Belgium, it could be hours or days, we just don't know."
Speaking on Wednesday afternoon, Deputy Chief Constable Pippa Mills said the lorry and the container were being moved to nearby Tilbury Docks so the bodies can be recovered while preserving the dignity of the victims.
"We are yet to identify them and must manage this sensitively with their families," she added.
Prime Minister Boris Johnson said the perpetrators of the crime "should be hunted down", while local MP Jackie Doyle-Price said the people smugglers responsible must be caught.
Police have said the tracking route used "will be a key line of inquiry".
The Bulgarian ministry of foreign affairs said the truck was registered in Varna in Bulgaria "under the name of a company owned by an Irish citizen".
Police originally thought the lorry had travelled to the UK through Holyhead in north Wales on October 19 but later revealed that the trailer had come directly from the Continent.
A freight ferry service runs from Zeebrugge to Purfleet.
The discovery comes as the National Crime Agency said the number of migrants being smuggled into the UK in containers and lorries has risen in the last year.
