Custody Bank of Japan Ltd. will set up a second panel of outside lawyers to probe alleged misconduct by its former top executive, according to people familiar with the matter.

The move by the bank, whose major shareholders include Sumitomo Mitsui Trust Holdings Inc., came after the regulator deemed the initial investigation conducted by a similar panel in January to be unsatisfactory.

In June, the bank said it found improper conduct by an unidentified former top executive and was in contact with authorities for potential criminal offenses. The executive is Yoshikazu Tanaka, who was president of the company until the end of December, Bloomberg has reported. Tanaka has denied any wrongdoing.

The Financial Services Agency has ordered Custody Bank and Sumitomo Mitsui Trust to submit reports on the matter, Bloomberg reported in July. Custody Bank safeguards about 652 trillion yen ($4.4 trillion) of assets for investors.

After receiving the reports, the regulator saw issues with the bank’s first investigation, including that the panel didn’t interview Tanaka, said the people, who asked not to be identified because the information is private. The FSA asked it to conduct another probe with a fresh panel to ensure objectivity, the people added.

Officials at the FSA and Custody Bank declined to comment.

Custody Bank is 33.3% owned by Sumitomo Mitsui Trust and 27% by Mizuho Financial Group Inc., according to the custodian’s disclosure report. The rest is held by Resona Bank Ltd. and major Japanese insurers.