[First Man Down]

More likely they installed the game in their own PCs. If you're key doesn't work online you'll know for sure.

Confront the manager and tell him your suspicions (He's probably responisble, anyway). Tell him you'd like to register a formal complaint. You might scare him enough to stop, or it might get him to investigate if he's innocent. You never know, he may be aware of other instances.

A manager of our local EB was fired after he was caught pilfering thousands worth of games, consoles, etc.