A 25 year-old man appeared in court Monday charged with the manslaughter of 39 people found dead in a truck in Essex.
Officers found the bodies in a lorry container in Grays, a port on the River Thames, east of London.
Maurice Robinson, from Northern Ireland, was placed in custody at Chelmsford Magistrate's Court. He has been charged with 39 counts of manslaughter, conspiracy to traffic people, conspiracy to assist unlawful immigration and money laundering.
He's set to appear at the Old Bailey on November 25.
Three other people arrested in connection with the deaths were released on bail on Saturday, while another man who police believe is of interest to the investigation was arrested in Dublin.
The world has been "shocked by this tragedy" wrote British Prime Minister Boris Johnson in a book of condolences on Monday.
Home Secretary Priti Patel told parliament the focus now was to bring the perpetrators to justice.
"The families of the victims at this incredibly difficult time are in all our thoughts and have my full sympathy. Nothing can undo the loss they have suffered. We owe it to them to identify those responsible and ensure that they face the full force of the law.
"I want to work with those families to ensure they can bring forward any evidence they might have to help solve this appalling crime," said Patel.
The process of identifying the victims is continuing and nationalities have yet not been confirmed, she added.
Patel said she received agreement from the Belgian authorities to deploy extra UK officers to Zeebrugge, Belgium.
Essex Police originally said those found in the lorry were "believed to be Chinese nationals", but after the Vietnamese Embassy in London said it had received calls from citizens fearing they had relatives on the truck, the force said that they could not "realistically speculate" on the nationality of the victims.