Supt Vincent O’Brien made the warning after a raid on McCullagh’s Jewellery store in the Letterkenny Shopping Centre.
Thieves got in through the roof of an adjoining shop and then broke their way through a partition in the jewellery shop.
Once inside the gang drilled holes into display cabinets and escaped with several thousand euro worth of necklaces and rings.
Gardai are not ruling out the possibility that the raid is linked to another break-in to the Cameo Jewellery shop in Donegal Town eight weeks ago.
Supt O’Brien said “Most likely there was a market for this and it could be on its way out of this country altogether.
“We are asking people who have valuables on the premises at night when they are locked up to leave them in a safe,” he said.
He again appealed for witnesses to Monday morning’s heist in Letterkenny to come forward.
Gardai are particularly anxious to speak to taxi-drivers in the area around 4am to contact them.
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