Mark needs to prove where he was to someone. Leo says that you can see where you've been by going to google.com/dashboard. Click on maps, then more, then timeline. If it's enabled in the application settings, you will see a history of where your phone has checked in within the network. It should go as far back as 18 months at least. If that isn't good enough, you could contact your carrier as they will have that information available. But that information is only available to law enforcement as they can get access to that information without a warrant. So using Google is your best bet.