Japanese prosecutors are expected to arrest the country's best-known activist shareholder, fund manager Yoshiaki Murakami, as early as on Monday on suspicion of insider trading in a deal involving scandal-hit Internet firm Livedoor Co, Kyodo news agency reported on Sunday.
Quoting "sources familiar with the case", Kyodo said Tokyo prosecutors would arrest Murakami after receiving approval from the Supreme Public Prosecutors Office and the Tokyo High Public Prosecutors Office.
Japanese media have reported that prosecutors were investigating Murakami and the fund over its connection to a high-profile take-over battle last year initiated by Livedoor.
Prosecutors were not immediately available for comment.
Kyodo said on Saturday that prosecutors and financial regulators had questioned Murakami over possible insider trading in connection with his investment fund's purchases of shares in Nippon Broadcasting System Inc (NBS), a radio broadcaster affiliated with Japan's largest private media group.
Livedoor's former president, Takafumi Horie, and other executives were arrested in January and face charges of breaking securities laws in a separate business deal.
According to the reports, authorities were looking into whether Murakami knew of Livedoor's intention to launch a take-over bid for NBS.
Shares in NBS, in which the fund had bought a stake of at least 5 percent, surged after Livedoor launched its bid last February. The fund sold its shares at a profit to Livedoor and to market investors, the reports said.
NBS became a wholly-owned unit of Fuji Television Network Inc, Japan's biggest TV network, last year.
Murakami, a former official at Japan's trade ministry, has gained fame as a pioneer of Japanese shareholder activism. The aggressive pressure he puts on target companies to change the way they do business has caused waves in business circles.
Japanese shares fell in early trade on Friday on news of the probe but recovered later in the day on hopes that a recent market slid has ended.