Scotland's senior prosecutor has said a no-deal Brexit would "materially diminish" the country's ability to fight serious crime.
Lord Advocate James Wolffe said current arrangements with the rest of the EU are "particularly effective".
These include information sharing, joint investigations and the use of the European Arrest Warrant.
Both the UK and the EU have stressed the importance of continued cooperation.
Scotland's Brexit Secretary Mike Russell said he would argue for Scotland to remain part of Europol.
Mr Wolffe said a situation where the UK left the EU without an agreement on legal matters was of particular concern.
"On that worst case scenario, our ability to tackle cross-border crime and serious crime would be materially diminished," he said.
"Of course we cooperate with countries around the world but what we have in the EU is a set of arrangements that is particularly effective."
EU security commissioner Sir Julian King has been taking part in a serious of engagements in Scotland.
In a speech at Stirling University he said: "Finding the right way forward will be the challenge of the coming months. Just because something is desirable, does not mean it is straightforward.
"Just because it has political momentum, does not mean it will happen.
"There will be many knotty questions to untangle - including legal, technical, financial and political issues."
Cooperation among police and prosecutors in Europe is coordinated through organisations such as Europol and Eurojust.
Many of the arrangements are supervised by the European Court of Justice, although the UK government is determined to leave its jurisdiction.
Police Scotland works closely with Europol and senior officers have said that should continue.
Assistant Chief Constable Steve Johnson said: "The powers that we get through the EU, as being part of the EU and part of Europol, are hugely important in the arsenal we have.
"The spectre of not being part of Europol is one that looms large."
Police Scotland has an officer based at Europol headquarters in The Hague to help co-ordinate its work with other European forces.
Mr Johnson said he would "absolutely" want that to continue.
He added: "I think anybody in law enforcement would want to maintain the ease of that contact but also the operational effectiveness of that contact."
A Home Office paper on the issue says: "Consideration would need to be given to ensuring that any ongoing investigations would not be affected in such a way that criminals might escape prosecution or vulnerable individuals might be rendered less safe."
Prime Minister Theresa May has previously said she wants the UK to retain its security co-operation with Europol post-Brexit.
A number of countries that are not part of the EU, such as Norway, Switzerland and the US, have operational agreements with Europol that allow access to intelligence.
Speaking on the BBC's Good Morning Scotland radio programme, Scotland's Brexit Secretary Mr Russell said he would be arguing for Scotland, and the UK, to remain part of Eurpol.
"It's not quite as simple as that, though," he said.
"Certain things are only there for EU members. The European arrest warrant, which is immensely successful in Scotland, is absolutely crucial.
"This is yet another example of things happening that shouldn't happen.
"They are actually weakening our ability to do things in Scotland and we need to make that clear to the public. This is about the public knowing what the facts are."