Frankfurt: It was not a glamorous Hollywood-style bank heist. No tunnels. No repelling from helicopters. Not even a single ski mask.

Just an unusually heavy carry-on bag, which a female flight attendant struggled to carry through Frankfurt's airport after arriving from China.

But when curious customs agents took a look, they found evidence that may have helped them crack one of the biggest frauds in history against the Bundesbank, Germany's central bank. Authorities say the fraud has cost the bank about €6 million (Dh31.6 million).

Inside the flight attendant's bag, the authorities say, were thousands of €1 and €2 coins that had supposedly been scrapped after years of use but had been methodically reconstructed so they could be cashed in.

According to prosecutors, in recent years a fraud ring involving flight attendants has toted 30 tonnes of supposedly scrapped euro coins back into Europe from China.