There is always something very frustrating about Diet questioning of legislators involved in corruption scandals. So it was with Monday's inquiry of Mr. Fukushiro Nukaga, former economics minister, at a Lower House Council on Political Ethics. As expected, Mr. Nukaga, a Liberal Democrat, denied allegations that he had taken a bribe from the KSD mutual-aid foundation for small business. He merely repeated what he had said before, saying in effect that he is clean. Absent new evidence, grilling by opposition members fell flat.

The Liberal Democratic Party seems to believe that the Nukaga case has been effectively closed now that he has answered questions before the ethics panel. The fact is he has told nothing new about his alleged ties to KSD. The panel has done a poor job of investigating the case, in part because it has no authority to obtain testimony under oath. The Diet should call Mr. Nukaga as a sworn witness and find out what kind of role he had played in the money-for-favors scandal.

Mr. Nukaga is only one among various politicians accused or suspected of using political influence on behalf of KSD. Already a former LDP Upper House legislator, Mr. Takao Koyama, has been arrested. And a former LDP Upper House leader, Mr. Masakuni Murakami, had to resign from the Diet. The two men have received a lot of media attention, but Mr. Nukaga is no less important a figure in the widening corruption scandal.