I think you're missing the point. The issue here is that we have two prosecution regimes at work: one for the banks which works by more or less the rules you propose, and one for "everyone else", which very much doesn't. Your idea of only prosecuting bank employees with direct connection to the crimes seems like cold comfort to all the people threatened with arrest, in prison (or hell, even shot) because of the activities of their husbands and roommates.

Strangely, libertarian hacker types tend not to come to their defense as quickly as they do bank executives.