Kerviel, who told journalists on Friday he had gone through "hell" since the revelation in 2008 that SocGen had lost 4.9 billion euros ($6.5 billion) unwinding his risky bets, said that audio recordings used as evidence at his 2010 trial had been tampered with.
The lawsuit, if filed on Friday, will be the second in as many weeks leveled by Kerviel against SocGen ahead of his appeal, slated for June 4. Last week, Kerviel's lawyer David Koubbi filed a suit against SocGen for obtaining a verdict under false pretences and said on Friday he planned to file a second lawsuit. "We are filing a suit for forgery," Koubbi said.
For its part, Societe Generale dismissed the allegations, saying in a statement that Kerviel "was building media buzz" before his appeal. "This strategy aims to harm the image of the bank by taking elements from the court cases ... out of context or presenting them as new when they add nothing to the real issues."
Sitting in a converted Paris cinema and wearing an open-necked pink shirt, a steely faced Kerviel let his lawyer Koubbi do most of the talking.
Koubbi said earlier this month his team was given access to original audio recordings of Kerviel being interviewed by his superiors, a transcript of which was submitted as evidence. According to Koubbi, around half of the duration of the interviews had been cut.
"Over a total hearing time of 12 hours there are cuts totaling ... six hours," Koubbi said. "These tapes have been tampered with."
Kerviel said he clearly remembered saying to one of his superiors during these interviews that the bank was aware of his trades, something that SocGen has always denied. This was missing from the tapes, he said.
Kerviel, who has never denied he covered up his massive trading positions but has always claimed his superiors knew what he was doing, said he was confident the fresh evidence would help him win his appeal.
"These last four years have been hell," he said. "My name has been tainted and dragged through the mud."
The news conference comes a week after Koubbi said Kerviel would sue SocGen for obtaining a verdict under false pretences, a criminal charge that implies a party may have concealed evidence that contradicts the final verdict.
The sharply dressed, media-savvy Koubbi is known for representing high-profile clients like actress Isabelle Adjani and Tristane Banon, the writer who last year accused former IMF chief Dominique Strauss-Kahn of attempted rape in 2003. French public prosecutors dropped their probe due to lack of evidence.
SocGen, France's second-biggest listed bank, said last week and reiterated on Friday it would countersue for "false accusation" and promised to develop its position once Kerviel's appeal begins on June 4. ($1 = 0.7559 euros)
(Reporting by Lionel Laurent; Editing by Andrew Callus and Steve Orlofsky)
By Lionel Laurent