A senior detective has warned that policing faces a real challenge if quick and effective extradition laws are lost in the wake of Brexit.
Detective Chief Superintendent Hugh Hume told politicians at Stormont that negotiations on the split with Europe needed to protect a modern approach to the transfer of criminal and terror suspects.
He told the Justice Committee: "The loss of the European Arrest Warrant would be one of the main concerns that we would have."
The senior detective said that the UK made its second highest number of extradition requests to the Republic of Ireland.
"On the world stage, Ireland's is an important extradition treaty for the UK," he said.
"It's not just Northern Ireland. It's important to note it's the United Kingdom."
Mr Hume said the extradition issue with the Republic would be at the top of the list in Brexit talks involving British justice officials.
The PSNI detective joined Department of Justice officials at the committee as politicians explored the security, customs and policing issues that might arise in the wake of Brexit and how the border between the Republic and Northern Ireland would be affected.
Mr Hume also said it was too early to run a threat assessment on dissident terrorist activity or border security issues that Brexit may create.
"Until we really know what it's going to look like it'd be pre-emptive to start thinking about a threat assessment around the border," he said.
"At this stage it would all be aspirational. It's just too far off at the moment."
David Lavery, a Department of Justice official, said there was ongoing dialogue with officials in the Republic on the potential for Irish ports and airports to have UK immigration checks.
"There is an ongoing dialogue and it pre-dates Brexit between the UK and the Irish Republic about the movement of people," he told the committee.
Meanwhile, the Irish government's chief economist has warned around 40,000 people will lose their jobs in Ireland because of Theresa May's hard Brexit plan.
Exports to the UK are set to nosedive by nearly a third and €20bn will be heaped on to Ireland's national debt over the coming decade, it is predicted.
John McCarthy, chief economist at Dublin's Department of Finance, said much of the pain will be front-loaded over the coming five years but the fallout would continue afterwards.
He said the dire forecast was based on extensive economic modelling carried out by his own department and the Economic and Social Research Institute, a leading think tank.
"We know now that most likely scenario is a hard exit," he said, referring to the Prime Minister's speech on Tuesday laying out her blueprint for Britain's exit from the European Union.
"That would lead us to believe that the impact will be more severe," Mr McCarthy said.
Worst hit will likely be those working in the food and drink industries, as well as others whose business relies heavily on exports to the UK which could be slapped with punitive trade tariffs.