I have a very hard time grasping how someone can legally make that much money in that short a time frame.
It isn't certain he DID make that much money. The Feds sometimes like to make an example. In this case, they didn't catch all the perps; Eric Van Nguyen, for example, is still in the wind. And so they may blame a "mastermind" for causing all or most of the losses.
Babs did well. By all accounts, he really did have that Veyron. But far as I know, he never got any training in handling large amounts of money, so it wouldn't be surprising if he'd made mistakes.