An unfolding bribery scandal surrounding an insurance group for small business led to the resignation of Mr. Fukushiro Nukaga, state minister for economic and fiscal policy, on Tuesday. Just a week earlier, Mr. Takao Koyama, a Liberal Democratic member of the Upper House, was arrested on charges of receiving a bribe from the group, known as KSD. What is emerging is an extensive "money-for-influence" scandal reaching deep into the corridors of power.

The first order of business is to unravel the whole truth as soon as possible. Prosecutors have their work cut out. At the same time the Diet must conduct its own investigations to clarify the political and moral responsibilities of the politicians involved. Mr. Nukaga, among others, should be summoned for testimony. Prime Minister Yoshiro Mori, who appointed Mr. Nukaga to the key Cabinet post, cannot stand above the fray. The situation appears different from last year when, in a scandal involving payment of party membership dues, Mr. Kimitaka Kuze resigned as chairman of the Financial Reconstruction Commission. Then Mr. Mori pulled through without serious damage to his standing. This time the going may be rough.

Mr. Nukaga allegedly received a total of 15 million yen from KSD in November 1999 and April 2000 when he was deputy chief Cabinet secretary in the Cabinet of the late Keizo Obuchi. The money, it is reported, may have been a reward for his effort to help establish a technical university for small business. Mr. Nukaga has denied taking any bribe, saying that one of his secretaries received the money but returned it later. That sounds like a lame excuse. He has said nothing about why KSD gave him such a large amount of cash.