And you're still not answering my question as to what law she actually broke.
Here is the Comey quote that everyone seems so apoplectic about:
To be clear, this is not to suggest that in similar circumstances, a person who engaged in this activity would face no consequences. To the contrary, those individuals are often subject to security or administrative sanctions. But that is not what we are deciding now.
If you re-read what he is saying, his point is that the reckless actions would normally lead to punishment within the department, just like any employee can expect to be chewed out by their boss for making bad decisions. Assuming he is talking about legal action here directly contradicts what he said earlier about how in the past legal action has only been taken in extreme circumstances where the person showed clear intent that confidential documents be seen by people without clearance such as Patraeus showing documents to his mistress. The line "But that is not what we are deciding now" means that he is not arguing whether or not the State Department should internally punish Clinton, but whether there is grounds for legal action. Since she did not intend for documents to fall into unclassified hands, and there is no evidence that through negligence documents did fall into the wrong hands, there is not grounds to prosecute.