Police have searched two addresses in Northern Ireland as officers continue to question a Co Armagh man over the discovery of 39 bodies in a refrigerated lorry trailer.
The searches in Co Armagh on Wednesday night are believed to be linked to the arrest of the driver, named in reports as 25-year-old Mo Robinson, from Portadown.
He remains in custody for questioning by Essex Police on suspicion of murder.
There was no answer at the Co Armagh home of Mr Robinson's family.
Detectives have said the trailer containing the victims arrived at Purfleet from Zeebrugge in Belgium at around 12.30am on Wednesday and the front section to which it was attached, known as the tractor, came from Northern Ireland.
The lorry and trailer left the port at Purfleet shortly after 1.05am and officers were called around 30 minutes later after ambulance staff made the grim discovery at Waterglade Industrial Park in Eastern Avenue in nearby 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.
The Prime Minister 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 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.
Security checks for people smuggling are believed to be less stringent at both ports than at Calais and Dover.
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.