Polish police have started investigating possible foreign links in the short-lived theft of the sign above Auschwitz concentration camp in southern Poland last Friday.

Police swooped onto a gang of five Poles on Monday and recovered the German language sign, which reads "Arbeit macht frei" ("Work makes you free") - a cynical sign which greeted and gave false reassurance to millions sent there to be murdered by the Nazi Germans in World War II.

But no one believes they planned to keep the unique sign, nor to sell it on eBay or some other public platform. Instead, the theory has expanded that a Swedish-based collector may have ordered the item's theft. Police would not confirm nor deny that an international link is possible.

When police found the sign, it was twisted, cut into the three parts of the three words. Those who stole the sign, in their haste, left behind the letter "i" in the word "frei".

The men face up to 10 years in jail for stealing and cutting up the sign, which was made on Nazi orders by Polish prisoners at Auschwitz in 1940-41 and is on the UNESCO world heritage list.

Several people will share the reward money of 110,000 Polish Zlotys (around £22,000), offered by the Auschwitz museum, the police force and an anonymous benefactor for the recovery of the sign, according to police sources.

More than 1.5 million people, including Jews, Poles, Gypsies, political prisoners and social undesirables of the Third Reich, perished at the death camp of Auschwitz, the German name for the nearby Polish town of Oswiecim, during Nazi Germany's occupation of the country in World War II.

A replica sign has been hoisted above the entrance gate to the camp while the hunt for the real thing ensued. The Musuem which now governs the site, hopes to have the original restored in time for the 65th anniversary of its liberation by the Soviet Red Army in January.