A big reason why financial crimes are so hard to prosecute is that authorities often lack witnesses who can testify in detail about such crimes. That means prosecutors must rely on others forms of evidence -- like documents and emails. But even a pretty damning paper trail just doesn't have the punch of an individual pointing their finger and unloading all the sordid details. Also, without an insider to explain the labryinth of a typical securites fraud, it can be hard for prosecutors to ever even assemble such a trail.