All 39 migrants found dead in a truck trailer in Essex last month have been identified as Vietnamese their families informed, it was confirmed on Thursday, in a significant step forward in one of the UK’s biggest mass-death investigations.

Vietnam’s embassy in London announced all the dead were its country’s citizens in a statement shortly after Essex Police, the force in charge of the investigation, said it had completed identification of all the deceased, without disclosing any names.

A number of families in Ha Tinh and Nghe An provinces in central Vietnam have said they believe family members were in the trailer that was discovered on the Waterglade Industrial Park near Grays in the early hours of October 23. The region has been one of the main sources of people travelling clandestinely to the UK via smuggling networks, especially since an environmental disaster in 2016 devastated the area’s fishing industry.