The female flight attendant, who authorities said was not arrested because she had not redeemed any money, told them that Chinese friends had given her the coins to exchange abroad because domestic banks would not take them, according to Sing Tao, a Hong Kong newspaper.

All six suspects, ages 28 to 45, are being held awaiting trial, and so far none are cooperating with authorities, Ms. Möller-Scheu said. They face fraud and counterfeiting charges that carry maximum sentences of 10 years in prison. Under German law, the names of suspects are typically not released.

The fraud ring, which officials said had been operating since 2007, took advantage of the way the two-piece coins are made. The 2-euro coin has a nickel and brass alloy center, or “pill,” surrounded by a nickel and copper ring. The 1-euro coin has a copper and nickel pill surrounded by a nickel and brass ring.

When the coins were removed from circulation, a subcontractor separated the rings from the pills before the metal was sold to Chinese recycling companies.

Somehow, the thieves discovered that they could put the pills and rings back together, bring them to Germany and redeem them at the Bundesbank.

Prosecutors said they were just beginning to investigate how the scam worked in China. During raids of 10 buildings in and near Frankfurt on March 30, the police seized a machine that they think was used to reassemble coins. But Ms. Möller-Scheu said it was likely that most of the labor-intensive work of reassembling coins was done in China.