Days after the robbery at the Tefaf art fair in Maastricht, there is still no trace of the perpetrators.
Two temporarily detained men were released.
The search is in full swing, the police said.
The perpetrators probably stole jewels worth millions.
Investigators assume that professional thieves are behind the robbery.
They were obviously headed for the stand of a British jeweler.
The robbery on Tuesday morning also shocked the employees of the fair, said the general director of Tefaf, Bart Drenth: "We have never been through anything like this." The Tefaf, which ended on Thursday, is the most important fair for old art
On Tuesday, four armed men appeared in the exhibition hall.
Two of them smashed the jeweler's glass cases with a sledgehammer.
The other two held bystanders at bay with pistols.
The men had camouflaged themselves with beards, glasses and peaked caps.
After half a minute they ran away.
It is not clear how they managed to smuggle the guns and the hammer through the controls.
Nothing has been announced about the loot.
Media reports that it could be a necklace worth around 27 million euros.