The U.S. government is preparing a formal request for extradition of a Taiwanese man implicated in the slaying of a Chinese-American journalist in Northern California, the American Embassy in Rio de Janeiro said. Tung Kuei-sen was arrested in Rio on Sept. 20. Tung has been sought by the U.S. government in the killing of Henry Liu, 52, a writer for the Chinese-language San Francisco Journal, who was shot to death on Oct. 15, 1984, outside his home in Daly City. A U.S. Embassy source, requesting anonymity, said: "We have received confirmation from Brazilian authorities he was arrested for extradition purposes. The next step is to formalize the request, which we expect to do the first week in November." An alleged Taiwanese gangster, Wu Tun, 35, was convicted of murdering Liu by a Taiwan court earlier this year, as was Chen Chi-li, 42, reputed leader of Taiwan's powerful Bamboo Gang.