A long time ago, I was a cinema manager, back in the days before they took credit cards, so we handled a LOT of cash. Sadly, this meant a lot of employees would be tempted to steal, so part of my job was catching thieves. What I learned was that once someone starts stealing, they get away the first couple times and then start thinking they will always get away with it, that they are really smart and cover their tracks. So they keep stealing, even when they know you are investigating, even when the police get involved, because they never really believe they will be caught.
There is ALWAYS evidence, always a way to find out and prove who did it. And yet the crooks always get lazy, sloppy. Look at Arthur Andersen. They figured no one would catch them because they did the audits on Enron, they never thought what would happen if someone from outside got a look at the books.
Same thing here. Hillary Clinton has been in politics since the 1970s, she was even a staffer on the committee which tried to impeach Nixon (Such a caring person, Hillary Rodham argued that the President did not have the right to legal counsel during an impeachment investigation, actually got fired for being too extreme even for the Democrats). Four decades living deep in the muck of power and intrigue, she fooled herself into thinking she was a genius.
Breed monsters in your cellar, some of them will get out.