A Catholic mass was held on Sunday for Vietnamese feared among 39 people found dead in a truck in Britain, as families desperately awaited news about missing relatives who have not been heard from in days.The 31 men and eight women were initially believed to be Chinese, but several Vietnamese families have now come forward with fears their relatives are among the dead.The grim case has cast light on the extreme dangers facing illegal migrants seeking better lives in Europe. The driver of the refrigerated trailer discovered in an industrial park on Wednesday has been charged with 39 counts of manslaughter and people trafficking.Many of the suspected victims are believed to have come from impoverished villages in central Vietnam, a feeder of illegal migrants chasing promises of riches overseas. Worshippers gathered on Sunday in a remote town in central Nghe An province to pray for the missing, kneeling before a priest who delivered an emotional sermon. "We gather here to pray for all the 39 victims," priest Nguyen Duc Vinh said before a packed cathedral. "We don't know yet whether they were our children," he added as visitors sang hymns.Parents in the area have set up makeshift altars for their missing loved ones, many who have not been heard from since the truck was discovered Wednesday in Essex, east of London.Five people have so far been arrested in connection with the tragedy, the country's largest murder probe since the 2005 London suicide bombings.All the bodies have been sent to hospital to start the difficult task of identifying victims, who are believed to be undocumented.Waiting gameOn Saturday, 25-year-old Maurice Robinson from Northern Ireland was charged with 39 counts of manslaughter and conspiracy to traffic people. Robinson, who was arrested at the scene, also faces charges of conspiracy to assist unlawful immigration and money laundering.The charges came as Essex police said they want to fast-track the process of fingerprint identification and DNA testing, but warned it would take time.Vietnam's ambassador, Tran Ngoc An, visited police investigating the case on Saturday and also spoke on the phone to British interior minister Priti Patel, the embassy said.It is not clear if the complicated cross-border investigation could stretch to rural Vietnam, the first stop of transcontinental smuggling networks stretching thousands of miles from Vietnam into Europe. Relatives of the missing in Yen Thanh district of Nghe An province have been frozen with grief since news of the truck tragedy. The mother of missing 28-year-old man Vo Ngoc Nam said she last heard from her son days before the container was found. He messaged to say he was going to Britain from Romania, where he had been working for several months. "I have been waiting anxiously over the past few days for any news from him, but we got nothing," the stricken mother told AFP. Local officials visited her home yesterday to gather more information about Nam, as Vietnam's Prime Minister ordered government agencies to investigate illegal people smuggling from the country. Most of Vietnam's illegal migrants come from a handful of rural provinces in central Vietnam, where there are few jobs on offer and incomes sag well below the national average. Vietnamese migrants often embark on dangerous overland routes through eastern Europe en route to the UK, paying smugglers tens of thousands of dollars for the trips. Many end up working in Britain illegally, often in nail bars or on cannabis farms, heavily indebted and subject to exploitation.