German state prosecutors in Cologne revealed an inquiry is underway but have not yet named those under suspicion, reports the Financial Times.
Sal Oppenheim, which has recently been taken over by Deutsche Bank, has promised to cooperate fully with the probe so that "investigations can be concluded quickly and fully".
The private bank was hit badly by the financial crisis - recording its first loss since World War Two in 2008.
It recorded a $173 million deficit that year and was kept afloat by loans totalling $963 million from Deutsche Bank - paving the way for the eventual takeover deal that was agreed in late 2009.
Deutsche Bank has so far declined to comment on the ongoing probe into the activities of the former Sal Oppenheim managers.
By Gary Cooper