French bank Société Générale began investigating trades executed by Jerome Kerviel months before his activities were exposed in January, the Financial Timesreported.
The FTsaid it had learned that a senior executive of Fimat, then a wholly-owned subsidiary of SocGen, began investigating at the end of September deals executed by Fimat employee Moussa Bakir for Mr Kerviel after being alerted to abnormally high volumes on his broking desk.
The Fimat executive raised questions about commissions paid to Mr Bakir on at least four cash equities trades for Mr Kerviel.
But he uncovered nothing conclusive, and the inquiry was not prioritised as he prepared for Fimat's merger with Calyon Financial that created Newedge, the newspaper reported.
The investigation was still under way when SocGen discovered in January that Mr Kerviel had separately built up unauthorised futures positions totalling €50 billion ($73.43 billion), trying to cover his tracks with faked hedges.
The FTadded that it was unclear whether the Fimat inquiry into cash equities trading would have led to an alert sooner within SocGen, however.
In a separate interview, Bank of France governor Christian Noyer said he was more inclined to blame human error for the fact that Mr Kerviel's massive trades were not spotted rather than a culture of excessive risk-taking.