The truck in which 39 people died was in three towns and cities in Belgium and France in the days before the victims were taken to Essex, tracking data has revealed.
GPS data from the refrigerated trailer shows it also made two trips between the UK and mainland Europe between 16 October and 22 October, the day the bodies were found in an industrial estate in Essex.
The details of the movements of the trailer in the days before it made its final journey emerged as postmortems begin to establish how the 31 men and eight women died.
Eleven of the victims, whom police believe to be Chinese nationals, were taken by private ambulance to Broomsfield hospital in Chelmsford.
The Chinese ambassador to the UK, Liu Xiaoming, said he had sent a team to Essex to help police verify the identities of the victims. He added that their nationality was yet to be confirmed.
Detectives have been granted extra time to hold the lorry driver, Mo Robinson, on suspicion of murder.
Three properties in Northern Ireland have been raided since the discovery of the bodies on Wednesday and the National Crime Agency is working to establish if organised crime groups were involved.
The trailer was leased from one Irish company, the Monaghan-based Global Trailer Rental Europe, on 15 October to another business on the Irish border. It was the first time the second business had made such a leasing arrangement.
Sources have said that GPS data from the refrigerated unit shows that it left Monaghan on 15 October, before crossing into Northern Ireland, and then back south into the republic of Ireland.
It then travelled from Dublin port to Holyhead in north Wales overnight on 16 October, before crossing over to mainland Europe that evening.
It shows the trailer travelled to Dunkirk and Lille in France and Bruges. Dunkirk is 40 minute from Calais and is a known site for people-smugglers preying on migrants seeking to get across the English channel to the UK.
The data from the tracking device, which has been passed on to Essex police investigating the murders, also shows the trailer made two journeys between the UK and mainland Europe between October 17 and 22.
The data tracks the longitude and latitude of the trailer at all times and has been confirmed by sources.
In a statement released on Wednesday, GTR Europe confirmed it was the owner of the refrigerated trailer but it said it was entirely unaware of what the lessee used it for.
“The company has been in contact with police in Essex from early 23 October, immediately upon becoming aware that a trailer on lease from this company had been involved in this incident. Full details of the lessee have been given to the police,” a spokesman said.
The parents of the driver have been brought by police to England from their home in Northern Ireland to see him, the Guardian understands.
Mo Robinson, 25, a self-employed haulier from County Armagh, was detained after the bodies were discovered in the vehicle on an industrial estate in Grays, Essex on Wednesday.
On Thursday, magistrates in Basildon granted officers a warrant to hold him in custody for an additional 24 hours.
Their local councillor, Paul Berry, told Sky News: “His family are very well respected in the area and are very actively involved in community organisations.
“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.”
