The cargo ship at the centre of a Garda and Customs search was last night expected to leave Irish territorial waters and head to Portugal, according to reliable marine sources.
The MV Unique has previously been suspected of having illegal immigrants on board. It docked a mile outside DúLaoghaire on Thursday. It had no cargo and was not due to pick up any.
Detectives searched the ship for arms, drugs and illegal immigrants. Nothing was found. It is understood that the Unique did not request permission to berth in Dún Laoghaire.
An application is normally required several days in advance. Sources said no application had been made. The nine-strong crew of the Unique was "mainly Pakistani and a few Russians", other sources said.
Before the ship's reported decision to leave Irish territorial waters, Garda sources said their interest in the Unique had ended. "Our concern had been about persons wanting to disembark who may not have been entitled to do so. That concern has finished," they said.
"It is a small crew and so far immigration is not a major concern. If the crew wants to disembark they will have to be processed through immigration as is normal practice."
Some of the crew were reported to have wanted to leave the ship.
A spokesman for the International Transport Federation (ITF) in Dublin said the ship had been brought to its attention several months ago. There had been problems with wage payment for the crew and concerns relating to crew welfare and other "non-security-related" issues, he said.
On October 21st an ITF inspector had boarded the Unique in the German port of Kiel and sent a report to the organisation's London headquarters.
The ITF is awaiting instructions from its legal department. Although no inspector boarded the ship in Dún Laoghaire, the ITF locally had sent a report to London on the vessel's arrival in Irish territorial waters.
The 1,210-tonne Mongolian-registered ship has been tracked closely in an international operation in recent weeks. It has been travelling through European waters for more than a month without apparent reason.
A reliable marine source in Dublin said: "The Unique seems to be travelling without a cargo to pick up. Of course, there can be ships which for a while have no actual destination at sea, sometimes to avoid port duties. But it is rare for one to be at sea in such a manner for more than a month."
The ship was first spotted in European waters in April and then went missing until August. Since then, its movements have been closely monitored by marine authorities and immigration officials in several countries.
Last week it is understood to have been located off the French port of Cherbourg. It was later reported to have taken shelter off the south coast of England.