NHK has learned that Japanese police officials have questioned former executives of Ohsho Food Service on a voluntary basis. The police have also raided the family home of the company's founder. The moves are in connection with the 2013 murder of the firm's president.

Ohigashi Takayuki was shot in front of the company's Kyoto headquarters. Ohsho operates hundreds of Chinese restaurants across Japan and overseas.

Investigators arrested Tanaka Yukio on Friday. He is already serving a prison sentence for an unrelated shooting. Tanaka is a senior member of a "yakuza" gangster organization based in Fukuoka Prefecture.

Ohsho set up a third party panel after the 2013 incident. The panel said the company repeatedly conducted inappropriate deals with a business group, when the founder's family controlled the company. The deals included shady real estate transactions. The company reportedly lost more than 100 million dollars.

The panel said Ohigashi was trying to change the company's business practices.

Police are trying to determine whether the inappropriate deals are connected to Ohigashi's murder.

They are apparently trying to find out what was behind the incident by looking into the company's management practices at the time. They want to know whether there was any trouble that led to the murder.