Police are searching three properties in Northern Ireland after the bodies of 39 Chinese nationals were found in a lorry container at an Essex industrial estate.
The victims, which included 31 men and eight women, were discovered at Waterglade Industrial Park in Grays in the early hours of Wednesday.
Police said three addresses in County Armagh are being searched following the arrest of the lorry driver on suspicion of murder – and he remains in custody.
Sky sources named the suspect as Mo Robinson, from Portadown, and police said on Thursday they had been granted an extra 24 hours to question him.
The 25-year-old was driving the lorry before police were called to the scene in Grays at 1.40am, and officers have since begun the task of identifying those who died.
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His family are said to be "stunned" by news of his arrest and hope it is "a complete and utter mistake", having first found out when his picture appeared in the media.
Their local councillor, the DUP's Paul Berry, told Sky News: "His family are very well respected in the area and are very actively involved in community organisations.
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"Our heart goes out to them because as of yesterday morning they were not aware that he had been arrested."
He added: "The community's thoughts and prayers are with the family of the 39 people who have lost their lives. People are devastated but also stunned and shocked that someone local has been arrested."
Irish company Global Irish Rental said it owned the container and rented it out on 15 October, according to reports.
Belgian authorities believe the container was transported to the UK from the port of Zeebrugge at 2.49pm local time on Tuesday, arriving in Purfleet at around midnight.
CCTV has shown it being driven towards the industrial park at 1.10am, half an hour before Essex Police were called to the scene by ambulance crews.
The discovery of the bodies was among the worst of its kind in the UK.
In similar circumstances, the bodies of 58 Chinese people were found in a container at Dover, Kent, in 2000.
The Belgian public prosecutor's office said it is "not yet clear" when and where the victims were placed in the container, adding that no further information would be released at this time.
Its statement said it would continue to work with police in the UK to find out what happened – and the Chinese foreign affairs ministry has told Sky News it is also investigating the case.
Meanwhile, lorry driver Graham Westmorland told Sky News that scanners at Zeebrugge were not up to the job and people were able to get through without being picked up.
How the container ended up in Grays
Police believe the trailer travelled on a ship from the port of Zeebrugge in Belgium on Tuesday – where it was before then remains unclear.
From Zeebrugge it headed to Purfleet in Essex, arriving in the early hours of Wednesday.
Essex Police say the lorry cab began its journey to Grays in Northern Ireland, from where it headed to Dublin and then caught a ferry to Holyhead in north Wales.
It made its way to Essex and picked the container up from Purfleet at around 12.30am on Wednesday.
It left Purfleet at 1.05am and was driven to Grays, with CCTV footage showing the lorry driving towards the industrial park minutes before the bodies were found.
The images were taken at 1.10am and show the vehicle just around the corner from where the discovery was made a short time later at the estate.
Police have since moved the cab and refrigerated container to a secure location at Tilbury Docks and officers were seen bowing their heads out of respect for those who died as the lorry was driven out of the estate.
Essex Police said: "Each of the 39 people must undergo a full coroner's process to establish a cause of death, before we move on to attempting to identify each individual within the trailer.
"This will be a substantial operation and, at this stage, we cannot estimate how long these procedures will take."
China's UK embassy said: "We read with heavy heart the reports about the death of 39 people in Essex, England.
"We are in close contact with the British police to seek clarification and confirmation of the relevant reports."
Police are likely to be looking into the movements of the trailer, which is said to be fitted with a GPS tracking system.
The Bulgarian ministry of foreign affairs said the Scania truck was registered in Varna, on the east coast of the country, under the name of a company owned by an Irish citizen.
