(CNN) -- A man has been charged by police investigating the deaths of 39 people found dead in a truck trailer outside of London.
Maurice Robinson, 25, from Craigavon, Northern Ireland was arrested shortly after the bodies were found in an industrial park in Grays, Essex, on Wednesday.
Robinson is due to appear at Chelmsford Magistrates' Court on Monday charged with 39 counts of manslaughter, conspiracy to traffic people, conspiracy to assist unlawful immigration and money laundering.
Three other people arrested in connection with the investigation have been released, Essex police said on Sunday.
The three people released on bail are: a 38-year-old man and a 38-year-old woman from Warrington, both of whom were arrested in Cheshire on Friday, and a 45-year-old man from Northern Ireland who was arrested at Stansted Airport on the same day, Essex Police said.
Earlier Saturday, police said they would not speculate on the nationalities of those who died in the truck, but are aware of reports of missing individuals in the Vietnamese community.
"We cannot realistically speculate at this time about the nationalities of all of our deceased within that vehicle," detective chief inspector Martin Pasmore of Essex Police said.
UK authorities are working with their Vietnamese counterparts to identify the victims, but have not yet officially named any of them or confirmed their nationalities.
All of the victims' bodies have been transported from the trailer to Broomfield Hospital in Chelmsford for post-mortem examinations, according to Essex Police.
Pasmore said he had agreed with the Vietnamese Ambassador to the UK to a method of sharing fingerprints in the hope that it would help with the identification of the victims.
Essex Police have appealed for anyone who may have information about the 39 deceased to come forward.