Detectives also said they wanted to speak to any other Vietnamese nationals who had entered Britain illegally via a similar route through the port of Purfleet
British police said on Wednesday they had charged another man as part of their investigation into the deaths of 39 Vietnamese migrants found dead in the back of a truck near London last year.
Alexandru-Ovidiu Hanga, 27, was charged with an immigration offense and was due to appear later at Basildon Magistrates' Court, east of London.
Detectives also said they wanted to speak to any other Vietnamese nationals who had entered Britain illegally via a similar route through the port of Purfleet.
"We believe that a number of other people traveled into the UK in a similar way to the 39 deceased throughout the month of October and we hope that these people would be able to help us," Essex Police's Assistant Chief Constable Tim Smith said.
"We understand that they may be concerned about coming forward and sharing their experiences, but we can assure you that your information and details will be treated in confidence."
The victims, who included two 15-year-old boys, were discovered in October in the truck container on an industrial estate in Grays in Essex, about 20 miles (32 km) east of London.
Autopsies concluded that the provisional cause of death was a combination of hypoxia - oxygen deprivation - and hyperthermia - overheating - in an enclosed space.
Maurice Robinson, the driver of the truck who comes from Northern Ireland, admitted last November plotting to assist unlawful immigration and acquiring criminal property, while detectives have also charged him and another man with manslaughter and human trafficking.
They are also seeking a number of other suspects.