$300 million was allegedly laundered through Credit Suisse Hong Kong banker Atsushi Doden yesterday flew back to Tokyo to face arrest for laundering money for a yakuza crime syndicate, as investigators continued to probe the biggest money-laundering case uncovered in Japan. The Credit Suisse private banker, 41, is alleged to have funnelled more than $300 million for Japan's biggest crime ring, the Yamaguchi-gumi. The money reportedly passed through the Hong Kong branch to bank accounts in Switzerland. Police believe Doden was only part of a wider 'dirty' money operation involving more than $3 billion, making it Japan's largest cross-border money laundering case. Diplomatic officials yesterday said they had escorted the Japanese citizen to Hong Kong airport for the flight to Tokyo, after forcing him to surrender his passport. 'After we ordered him to hand over his passport, he chose to go back to Japan and face the arrest warrant,' said Japanese consular spokesman Morio Matsumoto. 'He was issued with a one-way travel permit.' Mr Matsumoto said an arrest warrant for Doden had been issued in Japan on June 3, as part of a high-profile investigation into Japan's secretive and ruthless yakuza. Yamaguchi-gumi is the largest of several crime rings which dominate the Japanese underworld, making their money through gambling, drugs, the sex trade and loan-sharking. Credit Suisse said its officials were co-operating with authorities in Hong Kong, Tokyo and Switzerland, and had frozen one account linked to the crime syndicate in December. 'Things like this happen,' said Martin Somogyi, a spokesman for Credit Suisse based in Switzerland. Police allege billions of yen were sent to Credit Suisse accounts in Switzerland in the name of Susumu Kajiyama, 54, head of a loansharking ring linked to Yamaguchi-gumi.