Legal Question in Criminal Law in California

It is not clear from your question that you've broken any laws. Whether you have will depend on additional facts. It's also not clear whether the other people are being prosecuted yet, or how likely it is that you will be drawn in as a witness.

You may want to contact your local public defender's office for guidance. They will be better able to assess your risk, and may be able to help you become a confidential informant while shielding yourself from prosecution.

You don't need an attorney if you haven't committed a crime. It sounds like you want to be a good citizen and report a crime. You can contact the PD as Mr Hoffman suggested, or directly contact the police to offer 'confidential informant' information on condition your existence is kept confidential. As long as you don't disclose information that the 'ring' would be able to identify you by, your secret would be safe.