NHK has learned that two people linked to allegations of bribery of a Japanese lawmaker say they handed cash worth about 27,000 dollars to him. Tsukasa Akimoto denies receiving the money.
At the time of the alleged bribery, Akimoto held senior government posts dealing with integrated resorts.
Tokyo prosecutors arrested Akimoto on Wednesday on charges that include taking bribes in September 2017 from a Chinese firm, 500.com. The company was seeking to enter Japan's integrated resort business containing casinos.
Two advisers to the Chinese firm, Masahiko Konno and Katsunori Nakazato, and a former executive of its Japanese arm, Zheng Xi, were also arrested on suspicion of giving bribes.
Sources say two Japanese, including Konno, told investigators that they handed the cash to Akimoto in Tokyo in late September 2017.
Lower House elections were held the following month.
The prosecutors suspect that the bribe was a donation to his campaign.
A lawyer who met Akimoto at a detention center on Wednesday said he completely denies the allegations. Akimoto has left the governing Liberal Democratic Party.