resolve a security breach

I need a freelancer prove that a certain individual/company hacked my G-Mail account. Its my understanding with the right tools this can be done summary as follows: i set up a new gmail account for communication for a specific person/company. This person is the only individual in the world that has this e-mail address. No one has it. As further evidence, no other mail has been received other than the subject person/company This account was hacked, and the password changed twice. Is there anyway to catch this person? Even if you are able to locate the IP address that is gaining unauthorized access to your email account on your own, professional hackers will cover their tracks by hiding behind a proxy server. Also, an IP address does not give you the physical address of the email hacker; it only tells you the location of the ISP providing the connection to the hacker. This said, is there anyone out there that has tools or means of proving this person hacked my e-mail account?. thank you for reading and please ask any questions