In January 2008, French bank Société Générale announced it had lost 4.9 billion euros through the reckless actions of one of its traders, Jérôme Kerviel, claiming it had been unaware of his actions. Kerviel, who maintained from the start that his hierarchy knew what he was doing, received a jail sentence for forgery, fraud and hacking, and was ordered to pay the bank, in damages, the huge sum it lost. But last month, Mediapart can reveal, the former head of the French police’s financial crime squad, who led its investigation of the events and who was once convinced of the bank’s claims that Kerviel acted on his own, has given a statement to a French judge in which she details why she later became convinced, during her second investigation into the affair in 2012, the trader's bosses knew of his actions. Commander Nathalie Le Roy said she now feels she had been “used” by the bank in the 2008 investigation, how it later held back key evidence she requested, of witness accounts that Kerviel’s superiors were already made aware in 2007 of his extravagant trades, of allegations that Société Générale staff were made to sign gagging agreements and revealed that its claimed losses have never been independently verified. Martine Orange reports on a dramatic turnaround in the affair which appears bound to reopen the case.