Four people are now under arrest in connection with the incident.
Police in London have arrested a second Northern Irish man in connection with the discovery of 39 dead bodies in a lorry in Essex.
On Friday Evening, Essex Police released a statement confirming that another man from Northern Ireland had been arrested.
Deputy Chief Constable Pippa Mills said: "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.
"This is a fast-moving investigation involving significant police resources dedicated to finding out the truth about what happened to the 39 people found dead in the lorry on Wednesday."
Mills added that any commentary regarding the nationality of those inside the truck was "speculation."
The arrest follows the detention of a 25-year-old man from Northern Ireland who had allegedly been driving the lorry. Earlier today, a 38 year-old man and a 38 year-old woman from Warrington were also arrested on suspicion of conspiracy to traffic people and on suspicion of manslaughter.
All four remain in custody.
While it had been speculated that the truck arrived in the UK via Ireland, police now believe that the trailer travelled from Zeebrugge in Belgium into Purfleet in England, docking in the Thurrock area shortly after 12.30am on Wednesday.
