LONDON -- All 39 people found dead in a refrigerated container truck near an English port were Chinese citizens, British police confirmed Thursday as they investigated one of the country's deadliest cases of human smuggling.
The Essex Police force said 31 men and eight women were found dead in the truck early Wednesday at an industrial park in Grays, a town 25 miles east of London.
A magistrate gave detectives another 24 hours to question the driver, a 25-year-old man from Northern Ireland who has been arrested on suspicion of attempted murder. He has not been charged, and police have not released his name.
Police in Northern Ireland searched three properties there as detectives sought to piece together how the truck's cab, its container and the victims came together on such a deadly journey.
Pippa Mills, deputy chief of Essex Police, said the process of conducting post-mortem examinations and identifying the victims would be "lengthy and complex."
"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," she said.
The Chinese Foreign Ministry said Chinese Embassy employees in the U.K. were driving to the scene of the crime to aid the investigation.
Police believe the truck and container took separate journeys before ending up at the industrial park. They say the container traveled by ferry from the Belgian port of Zeebrugge to Purfleet, England, where it arrived early Wednesday and was picked up by the truck driver and driven the few miles to Grays.
The truck cab, which is registered in Bulgaria to a company owned by an Irish woman, is believed to have traveled from Northern Ireland to Dublin, where it caught a ferry to Wales, then drove across Britain to pick up the container.
Global Trailer Rentals Ltd told Ireland's national broadcaster RTE on Thursday that it owns the trailer and that it was leased Oct. 15 in County Monaghan, in Ireland, at a rate of $299 per week.
The Dublin-based company said it will make the data from its tracking system available to investigators.