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The guards called the bank but were told no one was expecting them. The guards became suspicious and looked in their briefcase, where they found the bonds, some of which had a face value of 500 million euros.
The Vatican police called Italian police, who searched the men's hotel and found rubber stamps, embossers and other instruments for making counterfeit bonds.
The Dutchman was found to be carrying three passports, all valid, a Vatican security official told Reuters.
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Police had kept the arrests quiet, apparently to continue their investigation of the men, but the story was published on Sunday in Italian newspapers.
The Corriere della Sera newspaper said some of the bonds and accompanying documentation had grammatical errors in English and letters of guarantee which referred to the late U.S. President John F. Kennedy and his late brother Robert F. Kennedy.
Media reports said the pair had been freed pending further investigation. The Corriere della Sera also said the Dutchman had been arrested two years ago in Hong Kong on fraud charges.
A Vatican spokesman and a Vatican security official both described the men as "naive".
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