Activist investor Yoshiaki Murakami has been questioned by the securities watchdog on a voluntary basis on suspicion of manipulating share prices of apparel company TSI Holdings Co., sources close to the matter said Thursday.

On Wednesday, the Securities and Exchange Surveillance Commission questioned Murakami and his daughter Aya, who heads investment firm C&I Holdings Co., the sources said. Investigators also searched the premises of C&I and other locations related to Murakami.

The SESC suspects that Murakami rigged the share prices of companies other than TSI Holdings and may file a criminal complaint against him, the sources said.

Murakami is known for his Murakami Fund, which became widely known for demanding tough managerial reforms at major companies it invested in.

The fund, which at its peak is said to have managed over ¥400 billion in assets, was disbanded after Murakami was arrested in 2006 on suspicion of insider trading in Nippon Broadcasting System Inc. shares, for which he was later convicted.

The 56-year-old former bureaucrat is now suspected of manipulating share prices in TSI Holdings, set up in 2011 through the integration of Tokyo Style Co. and Sanei-International Co., the sources said.

The SESC suspects Murakami artificially weakened the price of TSI Holding shares by submitting massive sale orders in June and July last year, and then bought the shares again to sell for profit when their price went up.

In 2002, Murakami was effectively Tokyo Style's major shareholder and fought a battle against the company's management, demanding managerial reforms that included a hike in dividend payouts.