JÉRÔME KERVIEL was able to build up €50 billion in unauthorised futures positions at Société Générale because of "fragmented" internal controls, a report commissioned by the bank said yesterday.

Unwinding those positions cost a record €4.9 billion, a loss the bank blamed on the 31-year-old former trader, now at the centre of a criminal investigation into the affair, news agencies reported.

The report was commissioned by the board and led by a three-person committee headed by Jean-Martin Folz, former chief executive of PSA Peugeot Citroën, into how Mr Kerviel was able to place the trades.

Mr Kerviel's assistant, who was not named in the report, performed 15 per cent of the fictitious trades used to cover the unauthorised positions and was "aware" of the fictitious trades, the report said.

Thomas Mougard, Mr Kerviel's assistant, is one of two people named by the judges leading the criminal probe as a material witness in the case. Mr Mougard denied he knew the trades were fictitious when questioned.

Mr Kerviel, who was released from prison on bail in March, is being investigated for forgery, breach of trust and unauthorised use of a computer in connection with unhedged transactions.

He is claiming corporate negligence in his defence