Prosecutors have asked former top government spokesman Hirokazu Matsuno and other executives of the ruling Liberal Democratic Party's largest faction, including Diet affairs chief Tsuyoshi Takagi, to submit to voluntary questioning over a political funds scandal, sources close to the matter said Thursday.

Matsuno stepped down as chief Cabinet secretary last week amid allegations he failed to report more than 10 million yen ($70,000) in income from tickets he sold for fundraising events hosted by the intraparty group, the sources said.

Matsuno served as secretary general of the intraparty group, a position widely viewed as one that would have involved knowledge of the flow of money, for two years through 2021. Takagi has been in the position since August 2022.

Japanese Chief Cabinet Secretary Hirokazu Matsuno (C) is surrounded by reporters upon arriving at the premier's office in Tokyo on Dec. 14, 2023, amid a political fundraising scandal involving himself and other ruling Liberal Democratic Party lawmakers belonging to the party faction previously led by former Prime Minister Shinzo Abe. (Kyodo) ==Kyodo

The prosecutors suspect that the faction, formerly led by slain Prime Minister Shinzo Abe, funneled back to members, including Matsuno and Takagi, a portion of the party revenue they raised from ticket sales, with the amount believed to have totaled around 500 million yen over a five-year period through 2022, the sources said.

The majority of the 99-member Abe faction is suspected of having received money, according to the sources.

"We will firmly investigate the matter and appropriately respond to it," said Takagi.

The move comes after the Tokyo District Public Prosecutors Office's special investigation squad on Tuesday searched the offices of the Abe faction and another led by former LDP Secretary General Toshihiro Nikai on suspicion of violating the political funds control law.

They are seeking to build cases against accountants working for the factions, who have admitted to not reporting the income in political funds statements when they were questioned on a voluntary basis, according to the sources.

Questioning of Abe faction lawmakers has also begun on a voluntary basis.

The Political Funds Control Act requires an accountant to submit a report on income and expenditure, and failure to report can result in imprisonment for up to five years or a fine of up to 1 million yen.

Lawmakers could also be accused of committing a crime, such as in cases where they are thought to have colluded with the accountant responsible.

The political funds scandal emerged following a criminal complaint alleging five LDP factions, including the fourth-largest one that Prime Minister Fumio Kishida headed until earlier this month, underreported revenue from political fundraising parties.

LDP factions have traditionally set quotas for lawmakers on the sale of party tickets, usually priced at 20,000 yen. In some groups, if lawmakers surpass their targets, the extra funds are passed back to them as a type of commission.

To mitigate the impact of the scandal on his government, which has seen its approval ratings plunge to its lowest level since its launch in October 2021, Kishida replaced four ministers belonging to the Abe group, including Matsuno and trade minister Yasutoshi Nishimura, who also served as faction secretary general.

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