A British lorry driver on Wednesday pleaded guilty to the manslaughter of 39 people found dead in a refrigerated truck in southeast England. Northern Ireland man Maurice Robinson, 25, was arrested shortly after the bodies of 31 men and eight women from Vietnam were discovered in the truck in an industrial zone in Grays, east of London, in October. The lorry arrived on a ferry from the Belgian port of Zeebrugge in the early hours of October 23, carrying the victims, who included two 15-year-old boys. They died from lack of oxygen and overheating, according to post-mortem examinations. Police charged five men, who appeared at a virtual hearing via Skype at the Old Bailey on Wednesday. Robinson had already pleaded guilty to conspiracy to assist unlawful immigration and acquiring criminal property. British Romanian Gheorghe Nica, 43, and Romanian national Alexandru-Ovidiu Hanga, 27, Northern Ireland man Christopher Kennedy, 23, all deny the charges against them. Valentin Calota, 37, was not asked to enter a plea to the charge of conspiring to assist unlawful immigration. Migrants can pay smugglers up to $40,000 for the dangerous journey, an enormous sum in Vietnam, where the annual per capital income is around $2,400, according to the World Bank. The family of one victim, 26-year-old woman Pham Thi Tra My, said they had received a text message from her in the hours before she is believed to have died. "I'm sorry Mom. My path to abroad doesn't succeed. Mom, I love you so much! I'm dying because I can't breathe," she said in the message confirmed by her brother Pham Manh Cuong. The victims came from impoverished and remote corners of central Vietnam, a hotspot for people willing to embark on dangerous journeys in the hope of striking it rich abroad. Many are smuggled illegally through Russia or China, often owing tens of thousands of dollars to their traffickers and carrying falsified documents. They end up working off the books on cannabis farms or in nail salons.