Who?

Why have I never heard of this guy before? Have I been living under a rock?

Jerome Kerviel, wiki.

...has been charged in the January 2008 Société Générale trading loss incident, resulting in losses valued at approximately €4.9 billion.[2] Société Générale characterises Kerviel as a rogue trader and claims Kerviel worked these trades alone, and without its authorization. Kerviel, in turn, told investigators that such practices are widespread and that getting a profit makes the hierarchy turn a blind eye.

Current events notwithstanding, why, like Jose Canseco, do I tend to believe the guilty once they are found to be just that?

The Telegraph on the investigation.