Investigators searched the offices of the ruling Liberal Democratic Party’s Abe and Nikai factions on Dec. 19 over suspicions they failed to report large amounts of revenues gained from their fund-raising parties.

More than 10 investigators from the Tokyo District Public Prosecutors Office’s Special Investigation Department entered each of the two offices around 10 a.m. Additional investigators later joined the searches.

Prosecutors have questioned faction officials in charge of accounting on a voluntary basis to determine if the two factions violated the Political Fund Control Law.

They decided to search the factions’ offices to clarify the chain of command and other details, sources said.

“We deeply regret that the situation has reached such a stage,” LDP Secretary-General Toshimitsu Motegi said at a news conference on Dec. 19. “We take it seriously and will take necessary measures while keeping a close eye on future investigations.”

In a statement, the Abe faction said: “We sincerely apologize for eroding trust in politics. We will provide utmost cooperation to the investigation and respond to it with sincerity.”

The Nikai faction expressed the same sentiments in a statement issued in the name of its leader, Toshihiro Nikai, a former LDP secretary-general.

“We sincerely apologize for having caused concern and inconvenience. We will sincerely cooperate with requests from authorities and make efforts to resolve the matter,” the statement said.

The Abe faction, which was headed by former Prime Minister Shinzo Abe until he was fatally shot last year, and the Nikai faction have each held a fund-raising party once a year.

Member lawmakers were assigned quotas for sales of party tickets, which cost 20,000 yen ($140) each, depending on the number of times they had been elected and the position they held, sources said. If a lawmaker exceeded the sales quota, the faction returned the extra money to him or her.

Both factions recorded only the amount based on quotas as income on their political fund reports. Funds exceeding the quotas were not listed, the sources said.

The Abe faction, the largest in the LDP, is suspected of having failed to report about 500 million yen over the five years through 2022, for which the statute of limitations has not expired for such false reporting offenses, sources said.

The amount of money that went unreported at the Nikai faction exceeded 100 million yen, the sources said.

In addition, the Abe faction made it a rule not to list the money returned to lawmakers as expenditures in its political fund report, the sources said.

The lawmakers are also suspected of failing to record the money as income in the fund reports of their political organizations in accordance with the faction’s instructions, the sources said.

On the other hand, the Nikai faction reported the money returned to lawmakers as expenditures, and member lawmakers also reported it as donations.

Prosecutors began questioning Abe faction lawmakers on a voluntary basis on Dec. 16, three days after the extraordinary Diet session closed.

A large majority of the faction’s 99 members are believed to have received the money, the sources said.

Upper House member Yasutada Ono is suspected of having received more than 50 million yen, the largest amount, followed by Lower House members Yoshitaka Ikeda and Yaichi Tanigawa, with more than 40 million yen each, the sources said.

Seiko Hashimoto, former state minister in charge of the Tokyo Olympic and Paralympic Games, is suspected of having received about 20 million yen, the sources said.

Six senior officials of the Abe faction all received the money.

Hirokazu Matsuno, former chief Cabinet secretary, Tsuyoshi Takagi, chairman of the LDP’s Diet Affairs Committee, and Hiroshige Seko, secretary-general of the LDP’s Upper House caucus, are each suspected of having received more than 10 million yen, the sources said.

Koichi Hagiuda, chairman of the LDP’s Policy Research Council, and Ryu Shionoya, former education minister, each received several million yen, while Yasutoshi Nishimura, former economy minister, received about 1 million yen, the sources said.

The searches on Dec. 19 are believed to be the first on an LDP faction’s office in 19 years.

In 2004, prosecutors searched the office of the former Hashimoto faction concerning a behind-the-scenes donation worth 100 million yen from the Japan Dental Federation.