Two more people have been arrested over the deaths of 39 Vietnamese migrants found in the back of a truck near London last year.
Police in Essex confirmed today that a 22-year-old man had been arrested in Northern Ireland on Sunday on suspicion of manslaughter and facilitating unlawful immigration.
He is in custody in Essex.
Last week, British police along with German authorities detained Gheorghe Nica, 43, who was wanted on a European Arrest Warrant, at Frankfurt Airport.
Mr Nica, who lives near Grays, appeared in court on Saturday accused of 39 counts of manslaughter and one count of conspiracy to assist unlawful immigration and is due to reappear at London's Old Bailey court on 16 March.
The 39 victims, who included two 15-year-old boys, were found on an industrial estate in Grays in Essex, about 32km east of London in October.
They were mostly from Nghe An and Ha Tinh provinces in north-central Vietnam.
Post-morten examinations had concluded that the provisional cause of death was a combination of hypoxia and hyperthermia in an enclosed space.
Police have said the Vietnamese victims were found not long after the container arrived in Britain from Zeebrugge in Belgium.
The refrigerated unit was picked up at Purfleet dock and loaded onto a truck driven by Maurice Robinson from Craigavon in Co Armagh.
He has pleaded guilty in the UK to assisting illegal immigration.
Eamonn Harrison, from Mayobridge in Co Down, is facing 39 counts of manslaughter, conspiracy to assist unlawful immigration and conspiracy to commit human trafficking under the UK's Modern Slavery Act.
He is due back before the High Court tomorrow.