You can go from hero to zero in no time flat. I'm skeptical of how you obtained the boxes and boxes of evidence. Be careful there. Very careful because I'm certain I won't be the only person with that concern.
The response above is not intended as legal advice since it’s impracticable to provide thorough, accurate advice based upon the query without additional details. It is highly recommended that one should seek advice from a criminal defense attorney licensed in your jurisdiction by setting up a confidential meeting. Moreover, this response does not constitute the creation of an attorney-client relationship since this message is not a confidential communication because it was posted on a public website, thereby publicly disclosing the information, which is another reason to setup a confidential meeting with an attorney.
Report the tax fraud as suggested by my colleagues. If the IRS decides to investigate, you will be contacted by Special Agents of the Criminal Investigation Division. Give your documents to the Special Agents on the initial contact.