Kerviel, a Frenchman in his 30s, is at the centre of the fraud case uncovered last weekend. His lawyer Elisabeth Meyer said on French television network BFM that he 'is not fleeing' and is 'available for judicial authorities,' without specifying where he was.

Union officials representing employees at the bank - Mr Michel Marchet of CGT, Mr Alain Treviglio of CFDT and Mr Pascal Colin of CFTC - said managers who briefed them Thursday about the case told them that the trader was having 'family problems.'

Mr Treviglio said the trader 'might have lost his mind a bit.'

One of his former teachers, Ms Gisele Reynaud, described Kerviel as a 'brilliant' student. She taught him at a university in Lyon, where he graduated in 2000 after an intensive year-long course in how to track, monitor and keep account of the type of trades that he went on to do at Societe Generale.

She said the course was very technical and intense, and included accounting, information technology and law.

'He was a nice guy,' Ms Reynaud said. 'He was brilliant.'

The trader had worked for the bank since 2000 and earned a salary and bonus of less than 100,000 euros, executives said. The bank said he netted no personal financial gains from his operations.

Mr Marchet of the CGT said his union was concerned that Kerviel may have been trying to get spectacular results as a way to boost his bonus, and he said the system of bonuses for traders is 'something we want to talk about with management.'

'It's possible that he took positions with exaggerated risks, and when he had losses he tried to hide them - but with the stock market crisis, and an error that he seems to have committed, he was found out,' Mr Marchet said.

Kerviel has a page on the Internet site Facebook but no public photo posted.

A member of his lawyer's firm said on Thursday that Kerviel is 'not on the run'.

'He was in the law firm's offices today,' the source said on condition of anonymity. 'He is not on the run.'

Kerviel's lawyer, Ms Elisabeth Meyer, could not be reached by AFP, but she told French television station BFM-TV that her client was not in hiding.

'I want to specify that he has indicated he is not on the run, that he was at the disposal of the judiciary,' the lawyer said.

The 31-year-old trader was dismissed by the bank on Sunday and is 'waiting for written notification of the decision. He is not on the run,' she said.

Bank chairman Daniel Bouton told reporters on Thursday he did not know where the trader was located.

Kerviel worked in the investment bank division, moving from the middle office, which checked deals, to the front office or trading desk in 2005, a bank source added.

Mr Bouton said the rogue trader had used 'extremely sophisticated and varied techniques' to carry out 'fraud of a considerable scope.'

The Paris prosecutor's office opened a preliminary investigation into the scandal while scores of shareholders lodged suit against the bank for fraud and misconduct.

Outside the Societe Generale offices at Paris' La Defense business district, employees expressed shock, and several who had shares in the company said they were worried about their investments.

Mr Treviglio, of the CFDT, said staff were baffled as to how a lone trader with relatively little experience could have committed such large-scale fraud.

Since the bank insisted that Kerviel did not profit personally, Mr Treviglio struggled to understand his motives: 'Was it to hurt the company?' he wondered. - AP, AFP.