THE HAGUE, Netherlands (AP) — An international investigation is homing in on a gang of robbers believed to be responsible for a brazen multimillion-dollar jewelry heist at an art show in the Netherlands and two stolen gemstones have been recovered, Dutch police said Wednesday.

Smartly dressed robbers wielding sledge hammers snatched jewelry from display cases at an international art fair in the southern Dutch city of Maastricht nearly two years ago, triggering an international police operation to hunt them down and recover the loot that police say is worth tens of millions of dollars.

In their latest update on the progress of the investigation, police in the southern Dutch province of Limburg said they now have narrowed down the location of the robbers, who they previously said came from the Balkans.

“It is now clear that this concerns Serbia, more specifically the town of Nis. It cannot be ruled out that the suspects are currently staying there, but possibly also in Belgrade or the surrounding area,” police said in a statement.

The investigation team also said that a diamond taken from a necklace that was stolen in the robbery had been found in Israel and another in Hong Kong. Police last year reported the discovery of one of the diamonds, but at the time gave no further details.

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“Both diamonds have been seized for examination,” police said in Wednesday’s statement, without giving details of when the stones were recovered.

Police had previously revealed that they were hunting for four men and said Wednesday that a woman also is a suspect in the heist.

Two more women are under investigation for allegedly returning a rental car to a company near the airport in the German city of Frankfurt. The two women are “at the moment, not suspects in the investigation into the robbery,” police said.