i am no expert in this but look at what Nick Leeson has done to Baring Bank.

But its probably too early to judge this case yet. Even those on Wallstreet are having no clue about his intention. Some suggested that he was made a scapegoat to cover some bigger issue. Some feel it could be only a mistake in correlation input, because his action did not result in any loss from either his clients or DB. On the other hand, the shear amount (GBP 30m for a junior trader) plus the fact that it escape all internal control for 2 months suggest that things could be fishy. Well we have to wait and see.