The convicted rogue trader, Jerome Kerviel, has begun a three year jail sentence in France after being arrested late on Sunday.
He has spent years fighting charges stemming from massive market bets that nearly forced the closure of French bank Societe Generale in 2008.
His detention comes after he crossed the border in France from Italy.
For several weeks, Kerviel has been walking from Rome to Paris in protest against the “tyranny of financial markets”.
Kerviel had been required by French judges to report to a French police station by midnight to start serving his sentence, which was confirmed by France’s highest appeals court in March.
But when questioned by journalists as to why he has chosen to return now Kerviel said, “For the simple and good reason that I was never on the run, I’ve never wanted to run. I always wanted to take responsibility.”
Kerviel, 37, has never denied masking his 50-billion euro positions and maintains his bosses knew what he was doing.
It has become a high-profile case in France where he has been depicted as a poor individual struggling against a massive corporation.
Over the weekend, Kerviel appealed to the French President to give immunity to unnamed witnesses he said would be willing to testify in his favour against Societe Generale.