What you have there is not a device - it's a brick. There is no workaround for that problem because the system was designed to prevent stolen property being of any use to anyone except the owner.
If you know the G-Mail address that used to be on that device, go to G-mail.com and go through the Forgot Password process. Only you should know the answers to the security questions set up when the device was first registered.
If you don't know that much, please take it back to here you found it or hand it in to the local Police. Someone would probably like it back.