The 25-year-old truck driver is charged with manslaughter, conspiracy to traffic in people, aiding illegal immigrants and money laundering.
Police initially said the 39 victims were believed to be Chinese citizens, but later groups from Vietnam said they believed they were among the dead. Police said it would take time to verify the identity and nationality of the victims.
London -- thirty-nine bodies were found Wednesday morning in a container cooler about 25 miles east of London. Authorities said the dead were believed to be Chinese citizens.
This extraordinary case involves many countries, but there are far more questions than answers. The car was found on the main motorway around greater London, but it was registered in Bulgaria and had travelled by ferry from Dublin.
Even the police, who are leading the investigation, acknowledged in a statement on Thursday that "we are not going to get all the answers soon." Here's what we know and don't know about the case so far.
Who's in the truck?
Officials say there were 39 people on the truck, 31 men and eight women. They retracted an earlier claim that one of the dead was a minor.
The victim has not been identified. No names have been released, and representatives from the Chinese embassy in London are on their way to help identify them.
The circumstances surrounding the killings strongly suggest, but have not been confirmed, that they were trafficked and subsequently killed in accidents along the way.
How did the truck get to England?
Trucks and containers arrived in Britain from different ports, according to officials. The truck arrived in holyhead, wales, on Sunday by ferry from Dublin, while the container left zibrugge, Belgium, and arrived in the port of peverett early Wednesday, not far from where the body was later found.
Shortly after 1:05 a.m., the truck left peverett with the containers. About 30 minutes later, police arrived at an industrial park after receiving a call from a local ambulance service. Police did not say who called the ambulance.
It is not clear how the container arrived in Belgium. It was also unclear whether the 39 victims had been in the car before arriving in Britain, whether they had been in the whole journey together, how they reached European ports and where the truck was headed.
When will the victim be identified?
Police said a "full autopsy" would be carried out to determine the cause of death before investigators tried to establish their identities.
The process can be complicated because the victim may not be carrying identification.
How did they die?
It's still unknown.
If the reefer is started, people inside can freeze to death as the container can be as cold as minus 13 degrees Fahrenheit (minus 25 degrees Celsius). If closed, they could suffocate without ventilation.
There may be other factors that investigators have not identified or disclosed.
One person: the truck driver, a 25-year-old Northern Ireland man, has been arrested on suspicion of murder and remains in custody.
The police declined to identify him, but officials and the British news media identified him as Morris Robinson, also known as Mo.
No other suspects have been named and it is not clear who arranged to transport the victims.
It is also unclear whether Mr Robinson knew what was in the container. The containers are usually sealed and not opened until they reach the delivery point.
Separately, police said they had searched three properties in county armagh, Northern Ireland, in connection with the investigation. It was not immediately clear if any of the locations were connected to the driver.