Gardaí and UK police are working together in the hunt for two Irish brothers in the investigation into the deaths of 39 people found in the back of a lorry in Essex.
Officers yesterday appealed for information about the whereabouts of Ronan Hughes (40) and his brother Christopher (34), who are wanted on suspicion of manslaughter and human trafficking.
Ronan, also known as Rowan, is alleged to have rented the container in which the bodies were discovered, while Christopher owns a haulage firm.
They have links to addresses and firms on both sides of the Border.
Detective Chief Superintendent Stuart Hooper, who is leading the investigation on the UK side, said: "Finding and speaking to the Hughes brothers is crucial to our investigation."
An Garda Síochána's secretive crime and security section is attempting to track the movements of the brothers.
Last night it emerged gardaí had not yet received a European arrest warrant from UK authorities in relation to the suspects. This means gardaí have not carried out searches at a number of properties in Co Monaghan and Co Louth linked to the brothers.
"There has been no request for extradition, there has been no request for searches of properties," a senior source said. "This does not mean that gardaí are not involved in the manhunt for these individuals - specialist units are.
"Cross-Border co-operation is in place but no criminal offence has been detected or disclosed in the Republic of Ireland thus far," the source added.
Gardaí have also not yet received an extradition request from the Belgian or UK authorities for a man arrested at Dublin Port last weekend, who is currently on a protection regime in Cloverhill Prison in west Dublin.
The discovery of the bodies in a refrigerated truck on an industrial estate near London has shone a spotlight on the illicit trade that sends the poor of Asia, Africa and the Middle East on perilous journeys to the West.
The bodies were found in the early hours of last Wednesday, just over an hour after the container had arrived in Britain from Zeebrugge in Belgium.
On Monday, the truck's driver, Maurice Robinson (25), appeared in court accused of manslaughter and money laundering as well as accusations of conspiracy to traffic people and conspiracy to assist unlawful immigration.
For the latter alleged offences, the charge sheet stated he had conspired with Ronan Hughes and others, prosecutors said.