The link between the political world and the yakuza came out this week in a court statement by the public prosecutor at the beginning of a long-awaited case over the Sagawa Kyubin trucking company. The case involves about 500bn yen ( pounds 2.3bn) in fraudulent loan guarantees and bribes made by the company to other firms and to politicians.
This kind of corruption has become standard fare and on its own would have raised few eyebrows among the cynical electorate. But during their investigations the prosecutor's office also dug up evidence that executives from Sagawa were acting as go-betweens for Mr Kanemaru, the most powerful politician within the ruling Liberal Democratic Party (LDP), and the Inagawa-kai, the main yakuza gang in Tokyo.
The revelation of this 'circle of gold' linking politicians to crime syndicates is highly embarrassing to Mr Kanemaru and the LDP. 'Our country has been made to look ridiculous,' editorialised the Mainichi newspaper in Tokyo.
Mr Kanemaru resigned last month after admitting to accepting 500m yen as a gift from Sagawa. At the time he thought the matter would end there, and that after paying a small fine the scandal would die out. The last thing he wanted was awkward questions about gangsters.
The association between Sagawa and the Inagawa-kai had been known for some time - prosecutors think as much as one-fifth of the 500bn yen in loan guarantees was made to yakuza-affiliated firms. But the link with politicians, although suspected, had not been clearly established. Until this week.
According to the public prosecutor's statement, in 1987 'a politician' - widely recognised as a reference to Mr Kanemaru - contacted Hiroyasu Watanabe, the head of Sagawa's Tokyo office, with a sensitive request. Mr Kanemaru, in his position as kingmaker of Japanese politics, was trying to steer his ally, Noboru Takeshita, into the prime minister's post. But a hostile right-wing group, the Kominto, was making his task difficult by noisy street demonstrations designed to embarrass Mr Takeshita. Mr Kanemaru wanted the Sagawa boss to act as a middleman with the yakuza, to 'organise' an end to the anti-Takeshita campaign. Right-wing extremist groups and the yakuza have many close links.
Mr Watanabe, eager to please his political patrons, contacted the head of the Inagawa-kai, Susumu Ishii, the campaign against Mr Takeshita went silent and he duly became prime minister. 'It was as if Al Capone had helped a US presidential campaign,' said Tetsuroh Murobushi, an author and television commentator who specialises in political scandals. Since this revelation, and a further report that Mr Kanemaru used the yakuza connection on at least one more occasion to force a troublesome politician to resign, the press has been calling for direct questioning of Mr Kanemaru on his yakuza links.
So far Mr Kanemaru has brazenly refused to submit to questioning, contenting himself with a written admission that he accepted the Sagawa money, which he handed in yesterday.
Mr Murobushi says the deal between Mr Kanemaru and the Inagawa-kai in 1987 is the tip of the iceberg. Below the surface is a network of alliances between gangsters, right-wing extremists, LDP politicians and corporations. 'The yakuza and the right-wing groups overlap. And conservative LDP politicians and the right-wing groups often resemble each other. And there is a lot of financing from big companies.'
The foundations of this network were laid by one man - Japan's most infamous post-war intermediary between the yakuza and the LDP, Yoshio Kodama. Born in 1911 Mr Kodama was an ultranationalist who was designated a Class A war criminal but released in 1948. His money set up the Liberal Party, which later expanded into today's LDP, and he maintained very close links with the yakuza throughout his life, until he died in 1984.
Mr Kodama organised yakuza groups to put down trade union protests and also to silence left-wing demonstrations against the US-Japan Security Pact. At the same time he was one of the main intermediaries for Lockheed, which funnelled millions of dollars in bribes to Japanese politicians. The Lockheed scandal ended with the arrest of the then prime minister, Kakuei Tanaka, in 1976. Mr Kodama was arrested a year later, but prosecutors could only find charges of tax evasion against him.
After Mr Kodama's death he had no obvious successor and a partial vacuum developed between the LDP and the yakuza. Mr Watanabe may have had ambitions to fill this vacuum but by all accounts wanted too much too quickly. 'Sagawa was a fast-growing company, and it didn't know how to give a bribe in a very sophisticated way,' Mr Murobushi said. Its loan guarantees started to go sour as the bubble economy crashed, and as police and prosecutors started to investigate the company's affairs one question led to another, ending with the circle of gold round Mr Kanemaru.