Prosecutors and financial regulators have questioned well-known fund manager Yoshiaki Murakami on a voluntary basis over possible insider trading in connection with purchases of shares in Nippon Broadcasting System Inc. in 2005, investigative sources said Saturday.

The Tokyo District Public Prosecutor's Office has yet to make a final decision, but there is a growing possibility that investigators will search the offices of the Murakami fund and other relevant locations as early as Monday, the sources said.

Murakami was reportedly questioned by investigators from the prosecutor's office and the Securities and Exchange Surveillance Commission.