The current economic crisis in large part grew from honest businesses with a group of rouge capitalist that were willing to say anything to "demonstrate" a huge profit in order to justify even huger bonuses.

When AIG sold credit default swaps, they were selling insurance when they had no insurance (cash reserves) to sell.  That's fraud.
To recall a more familiar expression,
They wrote checks their asses could not cash.

The problem in proving it, is that it was not simple fraud.
The, cover they laid was pro forma at best, but they played the game.
Insurance relies on models, and AIG CDS traders most likely hired mathematicians and software engineers to build them models that would "justify" the bet. 

Of course the model relies on the input -- as long as property values continue to grow at 20%/year the CDS was a great bet!
Each party in the conspiracy had a pretty good idea what the collective was doing, but they could all claim they were just doing their jobs: making the sale, doing the math, providing market analysis - and the bonuses kept coming.

Without question, we know that these people participated in fraud in order to enrich themselves.  But proving fraud requires proving intent - and if you thought AG Gonzolez's performance was impressive. . . . . how many times to you really want to listen to "I don't know what I did or why I did it" . . . only to learn that even if you could get a fraud conviction they already spent all their money on ice sculputure and hookers.