This was a bit more information than I expected. I was looking just for the actual evidence of hacking. It sounds more like there was a security hole planted within someone's computer. It's also possible it was done via email or by some backup access (forwarded emails, easily guessed password or password reset policy). The fix for this kind of fix for this kind of exploit is to close every potential hole but it seems like you do not know what the security hole is yet.
If you want to persue legal action, then the police and FBI are the people to contact. Just remember cases like this usually a while (evidence, warrant, trial).
In the meantime, if you need further assistance, feel free to email me and I can give you more info about your security options and solutions for your case.