The lorry was discovered in Essex in the UK and is believed to have begun its journey in Belgium

A Northern Irish lorry driver has been arrested on suspicion of murder after 39 bodies were discovered in the back of his truck outside of London in the early hours of October 23.

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Essex Police were summoned to the scene at Waterglade Industrial Park, Eastern Avenue, Grays in the UK after 39 bodies - 38 adults and one teenager - were discovered in the truck.

Reuters reports that the red cab unit of the truck is believed to have originated in Ireland. It had “Ireland” emblazoned on the windscreen along with the message “The Ultimate Dream."

Despite initial reports indicating that the truck originated in Bulgaria, police later confirmed that the trailer traveled from Zeebrugge, Belgium into Purfleet in Essex, England, and docked in the Thurrock area shortly after 12:30 am on October 23. 

BBC reports that the man arrested on suspicion of murder has been named locally as 25-year-old Mo Robinson, who is from the Portadown area of Co Armagh.

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Chief Superintendent of Essex Police Andrew Mariner said on Wednesday: "This is a tragic incident where a large number of people have lost their lives. Our enquiries are ongoing to establish what has happened.

"We are in the process of identifying the victims, however I anticipate that this could be a lengthy process. 

"We have arrested the lorry driver in connection with the incident who remains in police custody as our enquiries continue. I appreciate this cordon is going to disrupt the activity of local businesses in the area and we will work to ensure that disruption is kept as short as possible. We are working with Thurrock Council to mitigate against any impact our investigation scene will have locally."

In a later statement, Deputy Chief Constable Pippa Mills said: “Shortly before 1:40 am today we received reports that a number of people had been found inside a lorry's container at the Waterglade Industrial Park on Eastern Avenue in Grays. 

“Emergency services attended but sadly all 39 people inside the container had died. Early indications suggest that one of these people was a teenager, the rest are believed to be adults.

“A murder investigation was launched and the lorry driver, a 25-year-old man from Northern Ireland, was arrested on suspicion of murder and remains in police custody.

“At this stage we have not identified where the victims are from or their identities, and we anticipate that this could be a lengthy process.

“I would like to thank the local community and in particular those who have been directly affected by the police cordon at the industrial site. Thank you for your cooperation. I appreciate the impact the road closure will have on businesses within the cordon.

“I’m unable to say at this stage how long the cordon will be in place but please let me reassure you that my officers and partners will be doing everything they can to release the scene as soon as possible.

“This is an absolute tragedy and very sad day for Essex Police and the local community. We will continue to work alongside many other partner agencies to find out what led to these deaths.

“I would like to appeal for anyone who has any information to contact my officers at the Major Investigation Team on 101 or visit our website. We will update all of our channels as we are able to, but please appreciate we are in the early stages of what is likely to be a lengthy investigation.”

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On Wednesday, UK Prime Minister Boris Johnson said the incident was an "unimaginable tragedy and truly heartbreaking.

"I know that the thoughts and prayers of all members will be with those who lost their lives and their loved ones.

"I'm receiving regular updates. The Home Office will work closely with Essex Police as we establish exactly what has happened."

Reuters reports that Taoiseach Leo Varadkar said Irish authorities would carry out any investigations necessary if it was established that the truck had passed through Ireland.