Even if you haven't been charged with anything (yet), it is always a good idea to have your attorney present when being questioned by the police (especially if you have reason to believe that criminal charges are likely to be brought against you).
Ms. Berjis is licensed to practice law in the State of California. The laws of your jurisdiction may differ and thus this answer is for informational and educational purposes only and is not to be considered as legal advice. Since all facts are not addressed in the question, this answer could change depending on other significant and important facts. This answer in no way constitutes an attorney-client relationship.
You have evidence of a crime you want to turn over,having already reported something--but you're afraid you will be charged if you do, is that right? Recommend you meet with a criminal defense attorney before you do anything else.
NOT LEGAL ADVICE. FOR EDUCATION AND INFORMATION ONLY. Mr. Rafter is licensed to practice in the Commonwealth of Virginia and the US Federal Courts in Virginia. There is no implied or actual attorney-client relationship arising from this education exchange. You should speak with an attorney licensed in your state, to whom you have provided all the facts before you take steps that may impact your legal rights. Mr. Rafter is under no obligation to answer subsequent emails or phone calls related to this matter.
I suggest you talk to a lawyer if you have more evidence you like to disclosure, but afraid you could be charged if you do so. It's always better to talk to a lawyer and let her/him assist you in the preliminary stages rather than gave statement to law enforcement which may incriminate you. If you have more questions you can call or email me. Good luck.