The FBI document dump on the investigation shows that Hillary didn't know what a "C" meant in documents.
Clinton did not recall receiving any emails she thought should not have been on an unclassified system,” reads a summary of the FBI’s findings from July. “She relied on State officials to use their judgment when emailing her and could not recall anyone raising concerns with her regarding the sensitivity of the information she received at her email address.”
As Comey said before, three email chains with Clinton included at least one paragraph marked with a “(C),” indicating the paragraph contained confidential material.
“Clinton stated she did not know what the ‘(C)’ meant at the beginning of the paragraphs and speculated it was referencing paragraphs marked in alphabetical order,” according to the FBI summary.
This is a lie, and hows the FBI cover up. Everyone who is briefed on classified documents knows that they are marked according to a set standard of style. "C" always means "Classified". Clinton in signing any pre-tenure agreements on access to marked information would have been briefed on it. Specifically this guidance.
The title or subject of a classified document is marked with the appropriate classification abbreviation in parentheses -- (TS), (S), (C), or (U) immediately following and to the right of the title or subject. All documents containing information that requires control markings, regardless of classification, format, or medium, shall be portion marked. The overall classification of a document is equal to the highest classification level of any one portion found in the document.
Each portion of a classified document is to be marked with the appropriate classification abbreviation in parentheses immediately before the beginning of the portion. If the portion is numbered or lettered, place the abbreviation in parentheses between the letter or number and the start of the text. A portion is ordinarily defined as a paragraph, but also includes subjects, titles, graphics, tables, charts, bullet statements, sub-paragraphs, classified signature blocks, bullets and other portions with slide presentations and the like.
Again, she knows this by her NDA signing, acknowledging so.
So as you can see there is no excuse. There is no way the FBI didn't know this and include it in their findings UNLESS they know by doing so she be culpable and so subject to charges.
More at GP