I am a law school graduate currently awaiting Bar results. What I offer is mere information, not to be construed as forming an attorney client relationship.
Hmm, what is the line between tattle tale and civic duty? I think, if you have personally seen the crimes and know for a fact they are involving others and stealing (which affects store owners, consumers, and taxpayers in the long run), then perhaps you should tip the police. DO not expose yourself to possible harassment.
If you want to get more info, try contacting the d.a's office and asking about civic responsibility or moral duties (or lack of) without naming yourself.
Hope this helps.