Paramedics discovered the bodies of 39 people in a truck container at an industrial park outside London in the early hours of Wednesday morning. All victims -- including 31 men and eight women -- are believed by police to be Chinese nationals.
UK police appear to have established that the truck and its container followed two separate routes -- coming together towards the end of the journey shortly before the grisly discovery.
Here's what we know about the timeline so far, according to authorities in the UK and Belgium.
The truck itself is thought to have entered Great Britain through the Welsh port of Holyhead on Sunday after traveling over from Ireland, according to Essex Police. Investigators believe the truck -- which was registered in Bulgaria in 2017 -- originated in Northern Ireland.
The truck has not returned to Bulgaria since its registration, the country's prime minister, Boyko Borissov, said on local television channel bTV on Wednesday.
On Tuesday, the container arrived at the Belgian port of Zeebrugge at 2:49 p.m. local time (1:49 p.m. UK time), before leaving for the UK that same afternoon, according to the preliminary findings of Belgian prosecutors.
The container entered the English port of Purfleet in the very early hours of Wednesday. Essex Police believe it arrived shortly after 12:30 a.m. Belgian officials said the container arrived from Zeebrugge at midnight.
This is where the truck picked up the container, according to Essex Police, who said the truck then left the port shortly after 1:05 a.m.
At around 1:40 a.m., ambulance workers called police to the Waterglade Industrial Park in Grays following the discovery of the 39 people. All were pronounced dead at the scene. Authorities arrested the driver of the truck, a 25-year-old man from Northern Ireland, on suspicion of murder.
He was later identified by a local councilor as Mo Robinson. Paul Berry, the local councilor for Armagh (the area where Robinson resides in Northern Ireland) told CNN he learned of the arrest after speaking with Robinson's father. Police would not comment on the suspect's identify on Thursday.
On Wednesday evening, the truck and trailer were moved to a "secure location" in Tilbury Docks, about a 20-minute drive from where the bodies were discovered.
Later Wednesday, police in Northern Ireland raided multiple properties, one of which has been identified by local residents as the home of Robinson's parents. CNN was present at the parents' home in County Armagh, southwest of Belfast, and witnessed officers going in and out of the house.
Local residents have told CNN that the parents have since traveled to England to support their son.
Essex Police announced Thursday that the dead -- 31 men and eight women -- were all believed to be Chinese nationals. They also said that the truck driver would remain in custody for another 24 hours.
"This is an incredibly sensitive and high-profile investigation, and we are working swiftly to gather as full a picture as possible as to how these people lost their lives," deputy chief constable Pippa Mills said.
In Belgium, the Chinese embassy "demanded the Belgian police conduct a comprehensive investigation." Earlier in the day, China's embassy in the UK said it was sending personnel to the scene of the investigation "to verify relevant information."
On Thursday evening, Essex Police said the first 11 victims were transported to Broomfield Hospital in Chelmsford for postmortem examinations.
This story has been updated to correct the number of women found in the truck container.