Police are satisfied that the truck and container did not arrive via the Republic of Ireland.
Investigations continue following the discovery of 39 dead bodies inside the container of a lorry in Essex in the early hours of Wednesday morning.
Gardaí have been monitoring the investigation, seeking to establish if the lorry, which police initially believed came from Bulgaria and arrived in the UK via Holyhead on Saturday (19 October), may have used a ferry service from an Irish port before arriving in Holyhead.
An update from Essex Police states that, following further enquiries, they now believe that the trailer travelled from Zeebrugge in Belgium into Purfleet in England, docking in the Thurrock area shortly after 12.30am on Wednesday.
The tractor unit of the lorry, meanwhile, is believed to have originated in Northern Ireland.
Both the tractor unit and the container left the port in Thurrock shortly after 1.05am on Wednesday.
The alarm was raised around 30 minutes later after ambulance staff discovered the bodies inside the container at Waterglade Industrial Park in the town of Grays.
Gardaí are satisfied that the victims were not trafficked via the Republic of Ireland.
The driver of the lorry, a 25-year-old man from Northern Ireland, has been questioned by police following his arrest on suspicion of murder.
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