She texted her parents late on Tuesday night, UK time, when the trailer was in transit to the English port of Purfleet, according to Maritime tables seen by CNN. “I’m sorry Dad and Mom. The way I went overseas was not successful,” the 26-year-old wrote. “Mom, I love Dad and you so much. I’m dying because I can’t breathe. Nghen, Can Loc, Ha Tinh, Vietnam. Mom, I am so sorry, Mom.”It has not yet been confirmed that Pham Thi Tra My was one of the victims on the truck, but her family said they fear the worst. UK authorities are working with their Vietnamese counterparts to identify the victims but have not yet officially named any of them or confirmed their nationalities.Speaking to CNN in the family’s home in Vietnam, Pham Van Thin was still overcome with grief, saying it was “very painful” to receive the text. He said his daughter must have known she was going to die when she sent it. “I’ve lost both my loved one and my money,” Pham said, adding that the smugglers they paid did not tell the family how they would transport Tra My to the UK. She traveled to the country via China and France, but eventually fell out of contact with her family, after which Pham reported her missing. By then it was too late, Pham Thi Tra My and the other 38 people on board the truck were trapped and running out of oxygen. “The smugglers said that this was a … safe route, that people would go by airplane, car … if I had known she would go by this route, I would not have let her go,” Pham said. Nguyen Thi Phong said she is now dependent on the British and Vietnamese authorities to bring home their daughter. Neither she or her husband know whether they will ever get any of the money back they spent funding their daughter’s doomed journey. Four people arrestedMuch is still unclear about this tragedy, which came to light in the early hours of Wednesday morning UK time, when paramedics were called to a truck container at an industrial park outside London. Inside they found the bodies of 31 men and eight woman, all believed to be either Chinese or Vietnamese 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. They have arrested the truck driver, a 25-year-old Northern Irish man who met the container near where it was discovered, having driven from Northern Ireland via Wales. The container itself had traveled from the Belgian port of Zeebrugge. Three other people have also been arrested, as police in the UK and Belgium continue their investigations. They include a 48-year-old man in Northern Ireland, who was arrested on suspicion of manslaughter and of conspiracy to traffic people in connection to the investigation. A man and a woman, both 38 and from Warrington in northern England, were arrested on suspicion of trafficking and manslaughter, according to Essex Police.The driver remains in custody on suspicion of murder, police said.On Friday afternoon, more of the victims’ bodies were transported from the trailer to Broomfield Hospital in Chelmsford for post-mortem examinations, according to Britain’s PA news agency.”Formal identification processes will take place as well as the examinations to establish the causes of their deaths,” Pippa Mills, deputy chief constable from Essex police, told reporters. “This process is likely to be a lengthy one but it is crucial and we are working with her majesty’s coroner to ensure the dignity of the victims and the respect for their loved ones is at the forefront of our investigation.”This week’s investigation is a painful reminder of the tragic events in 2000, when 58 Chinese migrants were found dead in a lorry in Dover.Nguyen The Phuong reported from Ha Tinh, Vietnam. Sandi Sidhu and James Griffiths reported from Hong Kong. CNN’s Tara John, Bianca Britton, and journalist Phung Minh Tuan Anh contributed reporting.