Two people have been arrested in connection with the discovery of 39 bodies found in a lorry in Essex.
The man and woman, both aged 38 and from Warrington, have been arrested on suspicion of manslaughter and conspiracy to traffic people, police said.
The arrests were announced as it was claimed that the migrants, believed to be Chinese nationals, could have been trafficked by a Chinese “Snakehead” gang.
An international investigation is under way as post-mortem examinations were set to start on the bodies, which were found in a refrigerated trailer in Grays in the early hours of Wednesday morning.
It has also been suggested that the eight women and 31 men had most likely been dead for at least 12 hours in the refrigerated container.
Detectives have been given more time to question the driver of the truck, named locally as 25-year-old Mo Robinson from Northern Ireland, who has been arrested on suspicion of murder.
The task of moving the 39 bodies started on Thursday evening, with the first 11 victims moved by private ambulance with a police escort from the Port of Tilbury to Broomfield Hospital in Chelmsford, where post-mortem examinations will be carried out.
The remaining bodies are expected to be transported in stages, with police expecting all victims to be moved to hospital by the end of the week, warning the investigation will take “some considerable time”.
It has been suggested that the migrants, believed to be Chinese nationals, were dead before they arrived at Zeebrugge - more than 12 hours before they were found.
Mayor of Zeebrugge Dirk De Fauw, also the chairman of the port of Zeebrugge, said it was “virtually impossible” the victims went into the trailer at the Belgian border.
He told Belgian media: “Each trailer is systematically checked to look for outward signs of damage. Then it is sealed. Trailers are filmed until they are on the ferry.
“In the terminals too there are cameras. Breaking the seal, putting 39 people in a trailer and resealing the trailer without anybody noticing is virtually impossible.”
Joachim Coens, chief executive of Zeebrugge port, also said it was unlikely people were loaded into the container at the Belgian port.
He told Flemish TV channel VRT: "A refrigerated container in the port zone is completely sealed. During the check, the seal is examined, as is the licence plate.
"The vehicle is checked by cameras."
The trailer arrived at Purfleet from Zeebrugge in Belgium at around 12.30am on Wednesday, and the front section came from Northern Ireland via Holyhead in North Wales on Sunday.
The lorry and trailer left the port at Purfleet shortly after 1.05am and officers were called to the Waterglade Industrial Park on Eastern Avenue in Grays at 1.40am.
Robinson opened the doors to get some paperwork and passed out when he made the gruesome discovery, one witness told the Evening Standard.
Vigils have been held in London and Belfast to pay tribute to the victims and a book of condolences has been opened in Grays.
Essex Police Chief Constable Ben-Julian Harrington said he had the “utmost confidence” in his officers as the force leads its largest-ever murder investigation.
Irish police are also carrying out follow-up inquiries relating to the refrigerated container and the Irish-owned truck and three addresses have been searched in Northern Ireland.
Irish company Global Trailer Rentals Ltd (GTR) confirmed it owned the refrigerated part of the lorry, which had been leased on October 15 from its rentals yard in Co Monaghan, in the Republic of Ireland, at a rate of 275 euro (£237) a week.
A spokesman said the company was “shellshocked” and “gutted” by the news.
A spokesman for C.RO Ports, which operates terminals at Purfleet and Zeebrugge, said the firm would “fully assist” the police investigation, while the Chinese ambassador to the UK, Lui Xioaming, said the Chinese embassy had sent a team to Grays to meet with police.