Tokyo prosecutors indicted a former ruling Liberal Democratic Party lawmaker on Friday for allegedly failing to report millions of yen in political fundraising revenue, concluding an investigation into a slush fund scandal that has rocked the party led by Prime Minister Fumio Kishida.

The indictment of House of Representatives member Yoshitaka Ikeda, 57, rounded off a series of criminal cases against 10 lawmakers and accountants over violating the political funds control law. His secretary, Kazuhiro Kakinuma, 45, was also indicted.

House of Representatives member Yoshitaka Ikeda. (Kyodo)

The prosecutors, however, have not built cases against seven senior members of the party's largest faction at the center of the scandal, prompting a citizens' group to submit a request the same day that prosecutors review the cases against them.

"The LDP is trying to downplay the issue. We want a thorough review," said Yoshio Hayakawa, a representative of the group, at a press conference in Tokyo.

Ikeda belonged to the faction, whose undeclared funds are suspected to have totaled roughly 600 million yen ($4 million) in the five years from 2018.

He has allegedly received around 48 million yen from the faction's slush funds and colluded with his secretary to write down false revenue figures in the political funds reports of his fund-management body.

Ikeda, a former senior vice education minister, was arrested in January, with Tokyo prosecutors saying the action was taken out of fear that he could attempt to destroy evidence.

A source familiar with the matter said a computer at Ikeda's office was found to have been destroyed, possibly with a screwdriver.

At question in the scandal are funds raised by lawmakers for selling tickets for faction events beyond their assigned quotas. The excess funds were allegedly not reported while being distributed to the lawmakers.

While many in the LDP's largest faction, formerly led by the late Prime Minister Shinzo Abe, are suspected of having received the funds, the prosecutors targeted those who gained hefty sums.

The Political Funds Control Act requires an accountant to submit a report on income and expenditures, and a failure to report can be punishable by imprisonment for up to five years or a fine of up to 1 million yen. Lawmakers could also face criminal charges if suspected of colluding with accountants.

Since the scandal emerged late last year, a lawmaker, his secretary and an accountant from the Abe faction, as well as a former accountant of a faction led by former LDP Secretary General Toshihiro Nikai, have been indicted without arrest and will stand trial.

Another four, including a former accountant of Kishida's faction and a secretary of Nikai, were issued summary indictments and will not appear in court.

The Kishida and Abe factions are among the LDP's intraparty groups that have decided to disband in the wake of the scandal.

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Japan ruling party lawmaker Ikeda arrested over slush fund scandal