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You can see the most recent login activity if you scroll down to the bottom right of your gmail page and click “Details” under account activity, but that will only show you the most recent events. The only way I know to get anything additional is to go to security.google.com and check account activity there (https://security.google.com/settings/security/activity), but I still doubt you will be able to go back as far as you want. As far as I know, absent a court issued subpoena, that is the best you can do. Good luck, hope you get this taken care of.