Essex Police said in a statement on Friday that a fourth arrest has been made in relation to the 39 bodies found in a lorry in the UK on Wednesday

Friday afternoon update: Essex Police announced later in the day on October 25 that a fourth man, from Northern Ireland, has also been arrested, bringing the number of people in police custody to four.

Deputy Chief Constable Pippa Mills said in a statement“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."

DCC Mills added that they have not confirmed the nationalities of the 39 victims that were discovered on Wednesday morning.

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Earlier on Friday: Two people have been arrested on suspicion of manslaughter and conspiracy to traffic in connection to the tragic deaths of 39 people who were discovered in the back of a refrigerated lorry in England this week.

Read More: Armagh homes searched as investigation into death of 39 people found in truck continues

In an update posted on October 25, Essex Police, who are handling the incident, said: “We have carried out warrants in Cheshire as part of the investigation into 39 bodies being discovered in a lorry trailer in Grays.

“As a result, a 38-year-old man and a 38-year-old woman from Warrington have been arrested on suspicion of conspiracy to traffic people and on suspicion of 39 counts of manslaughter.

“A 25-year-old man, the driver of the lorry, remains in custody on suspicion of murder. A warrant of further detention was granted yesterday, Thursday 24 October, by local magistrates."

The Essex Police added that on Thursday, they began moving the victims' bodies to the mortuary at Broomfield Hospital in Chelmsford. The operation is being conducted in "close liaison" with the HM Coroner in order to "ensure that the dignity of victims and respect for their loved ones are at the forefront of our investigation."

The post-mortem examinations will begin on October 25, with formal identification to follow thereafter. Essex Police warned that the process will be "lengthy" but "crucial," and that their understanding of the situation may evolve.

Read More: Northern Irish man charged after 39 bodies discovered in the back of lorry

On Thursday, a spokesperson for the Irish company  Global Trailer Rentals Ltd (GTR) confirmed with RTE that it owns the refrigerated trailer where the 39 bodies where discovered.

The truck in question was rented on October 15 from the company’s yard in Co Monaghan.

Directors at GTR told RTE that they were “shellshocked” and “gutted.” They are reportedly cooperating with investigating police in providing GPS data.

In a statement, GTR said it was "entirely unaware that the trailer was to be used in the manner in which it appears to have been,” and that they contacted Essex Police as soon as they learned the truck was from their company.

Read More: Irish republican gang suspected in deaths of 39 Chinese in UK

On Friday, BBC reported that it was in contact with the families of three Vietnamese people who are worried their relatives may have been in the trailer.

The family of Pham Tra My, 26, said they received a text from her on Tuesday night saying she could not breathe. The family, who says they paid £30,000 for her to be smuggled to Britain, has not been able to contact her since.

Another family said they received a call from their 19-year-old female relative who said she was getting into a container and had to turn off her cell phone in order to avoid detection. Her family has not heard from her since, but a people smuggler has reportedly returned money to her family.

Another family is also said to have received their money back.

Two people have been arrested on charges of manslaughter and conspiracy to traffic in relation to the UK lorry deaths.Getty Images