How to prove my Gmail has been hacked?

Question

I believed that someone had hacked my Gmail because they were using information contained within my emails in an attempt to try to convince me that they were psychic. I told them that I didn't believe that they were psychic and knew they could only have obtained this information from reading my emails. I've not spoken to them since then, which was over a year ago. However, they have continued accessing my emails and they've been covering their tracks until recently. Recently, they've been forgetting to mark the emails they've read as unread after reading them, so when I loged in my new emails have already been read. Is there a way to prove that my Gmail has been hacked and file a police report especially being that I've already revoked access from devices and IP's that weren't mine?

This person is a self-professed hacker. When I told them that I knew they had accessed my emails they told me exactly how they had used a key logger back when we were working together to gain access to my account. My computer is secure now. All I need is to know now is how I can get information to file a police report.

Note: I don't have an account. I'm a public figure and I choose to be anonymous for a very good reason. Please stop removing my edits.

Answer 1

First things first, change your password and make sure the new password is secure (10+ characters, a number somewhere other than the last character, a capital somewhere other than the first character, not an iteration on your past password, etc). This is good to do periodically anyway.

GMail has tools for seeking suspicious account activity. Specifically, look at your recent security events, which should list all of your active logins plus all logins from the last four weeks, including locations and browser fingerprints (e.g. one of them will say "CURRENT DEVICE" to represent your browser right now. Are there others?).

Be wary about future attempts to obtain your credentials (somebody using your computer while you're logged in, a key logger, malware on your computer, or a phishing attack).

Answer 2

First, check the Account Activity Details link at the bottom of the webpage. Second, re-secure your account (change password, add 2-factor authentication,...)

This question deals with a similar situation of needing to re-secure a gmail account and check for unwanted access: Fell for phishing scam. Is my gmail account with 2-step verification vulnerable?

Answer 3

Proving someone that you suspect is responsible for hacking your google account is not only incredibly difficult not only for you gathering the information but difficult for any authority to follow up on it. Protecting yourself and your account should be your priority. Make sure you are using SSL for encryption and check out S/MIME as well.

However, if you do want to chase the rabbit down that hole. You could start by keeping an eye on IP tracker google provides for accessing your account. You could even put an image (web sites use a single pixel) within your email that is hosted on a server you have access to. If anyone reads your sent emails without disabling the images you can get their IP that way. You could even send yourself a zipped up piece of malware for your intruder to download.

Some of the trickery with pointing fingers at someone is, anyone can spoof anyone’s IP address. They could be getting that information directly from the online account, or having it sent to them via IMAP / POP. The latter of the two can use a separate application password as well. Not only that but, they could be getting that information another way, I.e MITM attacks which doesn’t require accessing your google account.