DETECTIVES investigating the deaths of 39 migrants found inside a lorry in Essex have made a fourth arrest, detaining a man at Stansted Airport.

The 48-year-old, from Northern Ireland, was held after the bodies of eight women and 31 men were discovered in a refrigerated trailer in Grays in the early hours of Wednesday, Essex Police said.

He was taken into custody on Friday on suspicion of conspiracy to traffic people and on suspicion of manslaughter.

A couple named locally as haulage boss Thomas Maher and his wife Joanna, both 38, were arrested on suspicion of 39 counts of manslaughter and people trafficking on Friday.

The driver of the Scania truck, named locally as 25-year-old Mo Robinson, from Northern Ireland, also remains in custody after he was held on suspicion of murder on Wednesday.

Essex Police initially believed all of the dead were Chinese nationals, but the force said at a press conference “this is now a developing picture”.

Deputy Chief Constable Pippa Mills said she would give no more details about the nationalities of the victims until formal identification had taken place.

Post-mortem examinations are due to begin as the bodies are moved by private ambulance with a police escort from the port of Tilbury to Broomfield Hospital in Chelmsford, Mills said.

If the fridge on the hermetically sealed trailer was not running there would be no air coming in, suffocating people inside, according to Richard Burnett, chief executive of the Road Haulage Association.

The BBC said it has been in contact with six Vietnamese families who fear their relatives are among the victims, with some having the smuggling fees repaid.

Relatives of 26-year-old Pham Tra My told the broadcaster they have not been able to contact her since she sent a text on Tuesday night saying she was suffocating.

“I am really, really sorry, Mum and Dad, my trip to a foreign land has failed,” she wrote.

“I am dying, I can’t breathe. I love you very much Mum and Dad. I am sorry, Mother.”

Her family said they had paid £30,000 for her to be smuggled into Britain, which has now been repaid.

Her brother told the broadcaster: “My sister went missing on October 23 on the way from Vietnam to the UK and we couldn’t contact her. We are concerned she may be in that trailer.

“We are asking the British police to help investigate so that my sister can be returned to the family.”

Nguyen Dinh Luong, 20, is also feared to be among the dead, with his brother telling the broadcaster Dinh Luong left Vietnam a year ago before spending time in France.

Ms Mills said at a press conference on Friday evening: “I can confirm we have officers working around the clock and we have now arrested a fourth person.

“A 48-year-old man from Northern Ireland was arrested at Stansted Airport earlier today on suspicion of conspiracy to traffic people and on suspicion of manslaughter.

“It follows the arrests of a 38-year-old man and a 38-year-old woman from Warrington during warrants executed in Cheshire overnight. They are currently in custody also on suspicion of conspiracy to traffic people and on suspicion of manslaughter.

“A 25-year-old man arrested on Wednesday on suspicion of murder remains in custody.”