(LONDON) — The 39 people found dead in a trailer in the United Kingdom are all believed to be Chinese nationals, police said Thursday.Emergency services were called to an industrial park in the town of Grays in Essex, southeast England, at around 1:40 a.m. local time Wednesday when the vehicle was discovered to have people inside. Thirty-nine people, 31 men and eight women, one of whom was a teenager, were pronounced dead at the scene. A 25-year-old man from Northern Ireland has been arrested on suspicion of murder in connection with the deaths, according to Essex police. The suspect has been named by British media, but this has not yet been confirmed by Essex Police who said they would not “speculate” about the identity of the suspect.Police in Northern Ireland are supporting the investigation and have raided three houses in connection with the incident, Essex police said. The trailer has been removed from the industrial park as authorities prepare for a coroner’s post-mortem examination. Each of the 39 individuals found dead must undergo a full post-mortem in order to establish cause of death before they can be identified, in a process police described as “complex and lengthy.”The U.K. Home Office, the government department responsible for domestic security and immigration, will also be working with Essex police and the National Crime Agency (NCA) on the investigation, the largest the country has seen since the 7/7 bombings. The NCA said they are working to “identify and take action against any organized crime groups who have played a role in causing these deaths.”The trailer entered the U.K. from the Belgian coastal town of Zeebrugge into the port of Purfleet, arriving at around 12:30 a.m. Wednesday, police said. The tractor unit traveled from Dublin, Ireland to Purfleet, where it collected the trailer. The tractor and trailer unit then left the port at around 12:30 a.m. on Oct. 23, before arriving at the industrial park in Grays, where the vehicle was discovered by emergency services shortly after.The Belgian Federal Public Prosecutor’s Office has opened a case into the incident and are working in “close cooperation” with British police.“The investigation will focus on the organizers of and all other parties involved in this transport,” the Prosecutor’s Office said in a statement. “It is not yet clear when the victims were placed in the container and whether this happened in Belgium.”The Bulgarian Ministry of Foreign Affairs issued a statement saying the Scania brand truck was registered in Bulgaria on behalf of a company owned by an Irish citizen.Richard Burnett, the chief executive of the Road Haulage Association, the trade body responsible for the needs of U.K. road transport operators, said the “tragedy … highlights the danger of migrant gangs people-smuggling on lorries.”Burnett told the BBC that the trailer may have been refrigerated, meaning temperatures could have reached as low as -13 F. Traffickers were increasingly using smaller ports as points of entry to the U.K., he said, as the security operations at larger ports such as the French port of Calais is more “robust.”Steve Valdez-Symonds, the Refugee and Migrants director of Amnesty International U.K., described the deaths as “heartbreaking and horrifying.”“People who are forced to take dangerous and sometimes fatal passages to reach the U.K. often do so because current immigration policies and practices deny them safe and legal options,” he said in a statement. “As the police investigation continues our thoughts remain with the families and friends of those affected by this awful tragedy.”It is the largest incident of this kind in the U.K. since 58 bodies were found in a truck at the English port of Dover in the year 2000.Copyright © 2019, ABC Audio. All rights reserved.