“Last I heard, they kept safety-deposit boxes there—which is what I assume this key unlocks.”

But investigators have yet to search a number of safety-deposit boxes and storage facilities linked to the suspects.

Two bank officials also said customers might be allowed to access their safety-deposit boxes and make non-cash transactions at bank branches.

They said they are confident some of these were items stolen during the burglary, when thieves broke into a vault containing safety-deposit boxes.

Demand for safety-deposit boxes is up, suggesting customers are hoarding foreign currency.