Armed garda detectives and the air support unit were involved in an arrest operation yesterday evening which led to the detention of a 40-year-old man who is wanted in the UK.
Essex police want to charge Ronan Hughes with multiple counts of manslaughter after 39 Vietnamese nationals were found dead in a lorry in Essex last October.
The haulier was arrested shortly after 5pm at his Co Monaghan home on foot of the European Arrest Warrant.
Mr Hughes was brought to Monaghan Garda Station "for processing" by members of the National Bureau of Criminal Investigation (NBCI).
He is due to appear before the High Court at an extradition hearing this morning.
In November, Essex police Detective Chief Inspector Daniel Stoten travelled to Belfast to make an appeal to Ronan and his brother Christopher Hughes to hand themselves in.
He revealed he had spoken to Ronan Hughes by phone.
Essex police have also been looking to question Christopher (33) but he was not the subject of yesterday's arrest operation.
Both Ronan and Christopher Hughes are subject to a major Criminal Assets Bureau (CAB) probe into the finances of haulage companies along the Border.
Thirty-nine Vietnamese people, including eight women and 31 males - including two boys aged 15 - were found in a refrigerated trailer in an industrial estate in Essex on October 23.
Some sent harrowing text messages to loved ones telling of their fears they may die.
Last month it emerged that a Northern Irish man alleged to have delivered the trailer in which the 39 migrants died will launch a legal challenge to his pending extradition in May.
Eamon Harrison (22), from Mayobridge, Co Down, is wanted to face 39 counts of manslaughter, conspiracy to assist unlawful immigration, and conspiracy to commit human trafficking under the UK's Modern Slavery Act.
It is alleged that Mr Harrison delivered the trailer in which the bodies were found in an industrial park in Grays, Essex, on October 23 last, to a Belgian port before its onward journey to Britain.
The High Court has heard that the sealed refrigeration unit was not turned on and the people inside died from oxygen starvation. Temperatures inside the unit rose to 38.5 degrees before it "steadily reduced", and police discovered "bloody hand prints" inside.
Maurice Robinson (25), from Craigavon, Co Armagh, was arrested by police at the scene and has admitted conspiracy to assist unlawful immigration and acquiring criminal property and the 39 manslaughter charges.