Many systems have audits.
A record written in a journal. Who signed on and when, what they looked at.
If Hillary was in Russia and someone is at her desk in the USA, signing in and emailing, a muslim sisterhood lover, the Chinese, God knows who else.... we have an audit trail of crimes. Even Bill Clintons server could have audits indicating crime.
So audit utilities of the system are probably being used to build a criminal case. You can’t lock up a former first Lady without rock solid proof, so I bet they are looking at more than we know.
In fact, I bet they now have proof of perjury.