Police in Vietnam's Nghe An province detained the individuals on Sunday on charges of organizing people smuggling overseas, according to the country's state-run newspaper, Thanh Nien.
During the early morning hours of Oct. 23, emergency services were called to an industrial park in the town of Grays in Essex, southeast England, when the vehicle was discovered to have people inside. Thirty-nine people -- eight women and 31 men -- were pronounced dead at the scene, which was about 20 miles east of London. Each victim appeared to have "a bag of some description, clothes, and other belongings,” according to Essex police.
“This is the largest mass fatality victim identification process in the history of Essex Police,” the department said in a statement on Oct. 26.
Essex police said the victims are all believed to be Vietnamese nationals, after initially saying they were thought to be Chinese.
Investigators are still working to identify all the victims and gather evidence "across a number of jurisdictions worldwide," according to Essex Police Assistant Chief Constable Tim Smith.
"At this time, we believe the victims are Vietnamese nationals, and we are in contact with the Vietnamese government," Smith said in a statement Friday. "We are in direct contact with a number of families in Vietnam and the U.K., and we believe we have identified families for some of the victims whose journey ended in tragedy on our shores."
The driver of the vehicle, 25-year-old Maurice Robinson of Northern Ireland, was arrested and has been charged with 39 counts of manslaughter, conspiracy to traffic people, conspiracy to assist unlawful immigration, and money laundering. His next court appearance is scheduled for Nov. 25, according to Essex police.
Another man from Northern Ireland, 22-year-old Eamonn Harrison, has been charged with 39 counts of manslaughter, as well as human trafficking and immigration offences. He appeared in court in Dublin on Friday and was remanded in custody, according to Essex police. The Crown Prosecution Service, the principal prosecuting authority for England and Wales, has started extradition proceedings to bring Harrison to England.
Three other suspects -- a 46-year-old man, a 38-year-old man and a 38-year-old woman -- were also arrested last week and questioned on suspicion of manslaughter and conspiracy to traffic people, but they have not been charged. Two were released on bail until Nov. 11 and the third has been bailed until Nov. 13, according to Essex police.
Meanwhile, detectives have urged two brothers from Northern Ireland to come forward and hand themselves in to police. Ronan Hughes, 40, and his 34-year-old brother Christopher Hughes are wanted on suspicion of manslaughter and human trafficking in connection with the case in Essex. The pair are believed to be in Northern Ireland but are also though to have links to the Irish Republic, according to Essex police.
ABC News' Alice Chambers and Guy Davies contributed to this report.