Fortunatly for this person, local laws at present are vague at best regarding hacking into someones email. However, it could be construed (at the DA's or CA's descretion) that this was an invasion of privacy which could lead to local charges being filed. The worst would be a misdemeanor charge being filed.

Proof of the alleged offense would be the burden of the procecutor. They would have to get telephone logs, server logs, etc... In addition, they would also have to prove intent.